ABSTRACTS OF CURRENT TECHNICAL LITERATURE IN ELECTRICAL ENGINEERING
1. CABLES, CONDUCTORS & WINDING WIRES
39676
Saxena N.K et.al
Cable fire stop system – A fire protection measure for cable galleries
Electrical India, Vol.51; No.11; November 2011; 152, 153, 156, 158, 159
Almost all the major industries such as power stations, fertilizer plants, cement plants, refineries, petrochemicals etc. use insulated electric cables extensively in bulk and long runs. Poly vinyl chloride (PVC) occupies a premier position in the field of able insulation and sheathing on account of its economy and its excellent electrical and handling properties, although it is self extinguishing by nature, in case of fire it may burn with copious amount of smoke and fumes of corrosive and toxic nature. Thus, these industries are immensely prone to fire accidents.
39677
Fothergill J.C.
The measurement of very low conductivity and dielectric loss in XLPE cables: a possible method to detect degradation due to thermal aging
IEEE Trans. on Dielectrics and Electrical Insulation; Vol.18; No.5; October 2011; 1544-1553
The dielectric response of crosslinked polyethylene (XLPE) insulated, miniature power cables, extruded with inner and outer semicons, was measured over the frequency range 10-4 to 104 Hz at temperatures from 20 to 100 °C. A dielectric spectrometer was used for the frequency range 10-4 to 10-2 Hz. A bespoke noise-free power supply was constructed and used to measure the dc conductivity and, using a Fourier transform technique, it was also used to measure the very low dielectric tanδ losses encountered at frequencies of 1 to 100 Hz. Tanδ measurements of <;10-5 were found in this frequency range and attributed to a β-mode dielectric relaxation lying above 100 Hz due to motion of chain segments in the amorphous region and an β-mode relaxation lying below 1 Hz window due to twists of chains in the crystal lamellae. The dc conductivity measurements were consistent with those of the dielectric spectrometer and indicate lower dc conductivities in vacuum degassed cables than have been previously reported for XLPE (less than 10-17 S.m-1). The conduction process is thermally activated with an activation energy of approximately 1.1 eV. Higher conductivities were found for non-degassed cables. A transformer ratio bridge was used for measurements in the range 1 to 10 kHz; loss in this region was shown to be due to the series resistance of the semicon layers. Thermal ageing of the cables at 135 °C for 60 days caused significant increases in the conductivity and tanδ and it is considered that such measurements may be a sensitive way of measuring electrical degradation due to thermal aging.
39678
Diego J.A. et.al
Annealing effect on the conductivity of XLPE insulation in power cable
IEEE Trans. on Dielectrics and Electrical Insulation; Vol.18; No.5; October 2011; 1554 - 1561
Conductivity (Σ) in XLPE insulation of power cables annealed at 90°C at temperatures between 50 and 97°C has been measured. In all cases there is an initial increase in conductivity that develops a maximum and finally decreases for long annealing times. This maximum appears in the sample annealed 20 days when conductivity is measured at 50°C and shifts gradually to higher annealing times up to 40 days when the measurement is performed at 97°C. A linear behavior of ln(Σ) versus T-1/4 is observed, which implies that the transport mechanism is basically via thermally assisted hopping conduction. Infrared spectroscopy indicates that, during annealing, some chemical species diffuse from the semiconducting shields (SC) into the XLPE. Thermally stimulated depolarization currents technique (TSDC) and intensity-current measurements (I-V) point out as well the presence of this diffusion process that becomes less significant after long annealing times. The initial increase in Σ is explained in terms of the increase in traps density due to the diffusion process from the SC shields. Long term decrease in Σ is justified by the observed decrease of diffusion rate for long annealing times.
39679
Jianying Li et.al
The effect of accelerated water tree ageing on the properties of XLPE cable insulation
IEEE Trans. on Dielectrics and Electrical Insulation; Vol.18; No.5; October 2011; 1562 - 1569
The influence of accelerated water treeing test (AWTT) on the properties of 10 kV cross-linked polyethylene (XLPE) cable insulating materials was investigated in this paper. The dielectric and physicochemical properties of both aged samples and unaged samples were tested. Dielectric property investigation found a new peak of the dielectric loss tangent with an activation of 0.14 eV in the low-frequency domain for aged samples. With increased ageing time, the conductivity in low frequency region of less than 50 Hz increases obviously, while it nearly keeps unchanged in the frequency above 50 Hz. Physicochemical investigation of FTIR, DSC, XRD and density measurement results indicated that AWTT ageing of XLPE insulated cables will lead to decreased crystallinity and density, and methyl group at the outer insulation layer cannot be found in aged samples. The melting temperature (Tm) was also decreased with ageing time. It was suggested that water was introduced from the outer layer of insulation and the degradation was developed by a combination of mechanical forces and electric force. During the ageing process, water will choose a path between surface of lamella and amorphous region, which consequently lead to the increase of low frequency conductivity and decrease of lamella thickness. Furthermore, a model was proposed to explain how the microstructure of XLPE cable insulation will change during AWTT ageing process. It is shown that XLPE cable insulation will be changed both in dielectric and physicochemical properties before any water tree was found, and a combination of dielectric and physicochemical methods is effective to detect the degradation of the XLPE cable insulation materials.
39680
Sato R et.al
Observation of water trees using terahertz spectroscopy and time-domain imaging
IEEE Trans. on Dielectrics and Electrical Insulation; Vol.18; No.5; October 2011; 1570 - 1577
Terahertz measurements were carried out to detect water trees grown in low-density polyethylene sheets. Water absorbs light at terahertz frequencies, fairly strongly at about 5.0 THz and rather weakly from 0.1 to 1.0 THz. Using the absorption at these frequencies, observation of water trees was tried according to the following procedures. First, we made a model sample, consisting of a polyethylene sheet, a water layer, and a copper plate, and terahertz light was irradiated to this sample vertically. The waveform and intensity of electric field of the terahertz light reflected by the sample clearly pointed out the presence of water layer beneath the polyethylene sheet by the reflection peak appearance time and the phase of reflected electric field. Secondly, water trees were grown in a polyethylene sheet, and terahertz light was scanned over the sheet. As a result, the intensity distribution of terahertz light reflected by the sample was in good agreement with the shape of the water trees. Observation of terahertz image was also carried out using the same polyethylene sheet with water trees over which a polyvinyl chloride sheet or a carbon-loaded polyethylene sheet was put to simulate the structure of a real cable. An image of water trees was also successfully observed. These results indicate that the terahertz spectroscopy can be a new characterization tool to observe the presence of water trees in a test sample taken from an aged cable.
2. ELECTRICAL MACHINES: MOTORS & DRIVES
2.1 Electrical Machines
39681
Limsuwan N. et.al
Novel Design of Flux-Intensifying Interior Permanent Magnet Synchronous Machine Suitable for Self-Sensing Control at Very Low Speed and Power Conversion
IEEE Trans.on Industry Applications, Vol. 47; No.5; Sept.-Oct. 2011; 2004 – 2012
This paper proposes a new rotor design for flux-intensifying interior permanent magnet synchronous machine (FI-IPM SM) that is more suitable for self-sensing control at zero/very low speed based on saliency-tracking methods and retains acceptable power conversion capability as compared to a traditional flux-weakening IPM SM (FW-IPM SM). Design steps for the rotor structure of the new machine are laid out and discussed to emphasize key design challenges. The proposed FI-IPM SM and a conventional FW-IPM SM with similar torque-speed capability are made to evaluate performances in power conversion as well as self-sensing capability at very low speed. Finite-element analysis (FEA) is used to evaluate each machine's performance. The proposed FI-IPM SM shows less variation in the saliency when the machine is loaded, leading to a possibility of better self-sensing performance at very low speed as compared to the traditional FW-IPM SM. Experimental results on the efficiency and self-sensing performance of these two machines are presented to verify the design methodology.
39682
Tischmacher H.et.al
Case Studies of Acoustic Noise Emission from Inverter-Fed Asynchronous Machines
IEEE Trans. on Industry Applications, Vol. 47; No.5; Sept.-Oct. 2011; 2013 - 2022
The issue of noise emission from electric drives is becoming increasingly important. Motor manufacturers have to comply with certain standards in order to assure the high competitiveness of their products. At the same time, with today's variable speed drives, which are supplied with nonsinusoidal voltages, the issue of noise reduction has become more complex. This is because the influence of additional factors, compared to machines supplied with sinusoidal voltage, must be considered over a wide speed range. The key to optimizing the machine's acoustic behavior is the thorough knowledge of the influence of the different noise sources and the excitation mechanisms over the complete speed range. Apart from the theoretical analysis and the simulation, an experimental investigation is necessary to obtain a better understanding of the previously mentioned factors and to minimize the machine's acoustic noise. This paper presents some characteristic case studies of acoustic noise emission in asynchronous machines supplied from voltage source inverters in order to examine the influence of diverse factors on the total noise level.
39683
Wrobel R. & Holliday D.
Thermal Modeling of a Segmented Stator Winding Design
IEEE Trans. on Industry Applications, Vol. 47; No.5; Sept.-Oct. 2011; 2023 – 2030
This paper presents a thermal analysis of a segmented stator winding design. As the thermal performance is one of the main factors limiting a machine's output capability, a thermal test on a complete prototype machine is an essential part of the design process. However, for the segmented stator winding design, a test-informed thermal analysis on a single stator tooth can be performed prior to the manufacture of the full machine. This approach allows for a rapid and inexpensive assessment of the thermal performance of the complete machine and early identification of design modifications needed. The research has been applied to the design of a highly efficient and compact permanent-magnet traction motor. A thermal model for a single tooth was developed and supported by tests to identify key heat transfer coefficients. A number of winding assemblies were compared, and the most promising was selected for the final motor prototype. The results from the approach are compared with thermal test results from the complete machine.
39684
Barcaro M. et.al
Six-Phase Supply Feasibility Using a PM Fractional-Slot Dual Winding Machine
IEEE Trans. on Industry Applications, Vol. 47; No.5; Sept.-Oct. 2011; 2042 - 2050
The growing interest in fault-tolerant drives requires new solutions avoiding the adoption of custom and expensive configurations. The machine with a dual three-phase winding is an interesting candidate. It is provided with two windings, each of them fed by one converter of half power. With a proper mechanical and electrical arrangement, the machine can be exactly a six-phase machine, obtaining higher performance during healthy conditions. In the event of a fault, one of the two three-phase windings (the faulty one) is disconnected, and the machine is operated by means of the healthy winding only. This paper analyzes the feasibility of this dual winding configuration applied to a nonoverlapped-coil fractional-slot winding permanent-magnet machine. The star of slots is applied to highlight the proper winding candidates. The more interesting windings are deeply analyzed.
39685
Grubic S. et.al
A New Concept for Online Surge Testing for the Detection of Winding Insulation Deterioration in Low-Voltage Induction Machines
IEEE Trans. on Industry Applications, Vol. 47; No.5; Sept.-Oct. 2011; 2051 - 2058
A breakdown of the electrical insulation system causes catastrophic failure of the electrical machine and brings large process downtime losses. Preventive maintenance and online monitoring are some of the methods to improve the reliability and to reduce unscheduled downtime. One of the main reasons for the failure of the machine is the breakdown of the stator turn insulation. The offline surge test is the most commonly used offline test to assess the condition of the turn insulation. There is no online monitoring method that is applicable to low-voltage machines and has the same capabilities as the surge test. This paper introduces new concepts to implement an online surge test. The possibilities and limitations of the online surge test are presented, as well as the simulation and experimental results, to validate the concepts.
39686
EL-Refaie A.M. et.al
Rotor End Losses in Multiphase Fractional-Slot Concentrated-Winding Permanent Magnet Synchronous Machines
IEEE Trans. on Industry Applications, Vol. 47; No.5; Sept.-Oct. 2011; 2066 - 2074
Fractional-slot concentrated windings (FSCW) have been gaining a lot of interest in permanent magnet (PM) synchronous machines. This is due to the advantages they provide including shorter nonoverlapping end turns, higher efficiency, higher power density, higher slot fill factor, lower manufacturing cost, better flux-weakening capability resulting in wider constant power versus speed range, and fault tolerance. This paper focuses on eddy-current losses in the rotor clamping rings. Additionally, the loss in the nonmagnetic shaft with the option of i) metallic, ii) nonmetallic, and iii) metallic with shielding laminations clamping rings is analyzed. The study is based on finite element analysis (FEA). Desirable slot/pole combinations for different number of phases with both single- and double-layer windings are investigated. Experimental results for a three-phase 12 slot/10 pole design are presented to confirm that the losses in the rotor clamping rings can be very significant in case of FSCW machines and should not be overlooked during the design phase.
39687
Shih-Chin Yang
Surface-Permanent-Magnet Synchronous Machine Design for Saliency-Tracking Self-Sensing Position Estimation at Zero and Low Speeds
IEEE Trans. on Industry Applications, Vol. 47; No.5; Sept.-Oct. 2011; 2103 - 2116
Elimination of externally mounted position sensors and their associated cables is a goal for drive manufacturers. This paper addresses design methods of surface-permanent-magnet (SPM) synchronous machines for saliency-tracking self-sensing (position sensorless) position estimation. Machine spatial saliency is created by stator magnetic saturation due to the rotor zigzag leakage flux from SPMs. Using the machine saliency created by zigzag leakage flux can allow an SPM machine to be suitable for saliency-tracking position estimation without the need of any special rotor design modification. In addition, another major benefit is achieved, i.e., a saliency role reversal whereby Ld >; Lq. This has the advantage of reducing machine cross-saturation and increasing the feasible region for closed-loop self-sensing control. All the design procedures are verified by the finite-element analysis, and a 50-W SPM machine is used for experimental evaluation.
39688
Jidin A
Simple Dynamic Overmodulation Strategy for Fast Torque Control in DTC of Induction Machines With Constant-Switching-Frequency Controller
IEEE Trans. on Industry Applications, Vol. 47; No.5; Sept.-Oct. 2011; 2283 - 2291
This paper presents a simple dynamic overmodulation method to obtain a fast dynamic torque response in direct torque control (DTC) of induction machines with constant-switching-frequency controller. A fast dynamic torque response can be obtained by switching only the most optimized voltage vector during torque dynamic condition. The optimized voltage vector can be identified by comparing the rate of change of torque produced between applications of two possible active voltage vectors, according to the flux position. The selection of the optimized voltage vector can be simply implemented by modifying the flux error status before it is being fed to the lookup table. It will be shown that the proposed switching strategy facilitates the DTC to perform under six-step mode to achieve the fastest dynamic torque response. The effectiveness of the proposed dynamic overmodulation to obtain the fast torque response is verified with some experimental results.
39689
Siu S. K. & Lopopolo, J.
Compatibility, Sizing, and Design Considerations for Generators and UPSs in Tiers I, II, III, and IV Topologies
IEEE Trans. on Industry Applications, Vol. 47; No. 6; Nov.-Dec. 2011; 2324 - 2329
Mission critical applications for data centers, financial institutions, telecommunications, and governments typically have generators and uninterruptible power supplies (UPSs) providing backup power to keep their critical information technology loads online. Tier I and tier II topologies according to ANSI/TIA-942 are very simple and straightforward with no redundancy or single distribution path with redundant components. Tier III and tier IV configurations have increasing complexity with multiple distribution paths, concurrent maintainability, and multiple active paths. This paper will explore the high-level compatibility, sizing, and design considerations for generators and UPSs in tiers I, II, III, and IV topologies.
39690
Dorrell D.G & Popescu M
Effect of Winding Asymmetries and Winding Connection on Small Synchronous Machines
IEEE Trans. on Industry Applications, Vol. 47; No. 6; Nov.-Dec. 2011; 2453 - 2459
This paper reports on the study of winding asymmetries in small synchronous generators. These types of generator are commonly used in diesel generator or back-up systems and are usually no more than a few or few tens of kilowatts with two, four, or six salient poles. The three-phase winding is 120 deg pitched, but often, lap windings are not used, rather, a hybrid of concentric winding and double layering is utilized. There are sound manufacturing reasons for this, and these are explained. This leads to small asymmetries in the phase-belt inductances and field-induced voltages. This is examined and validated experimentally. This paper discusses the techniques that are used to analyze the machine. These are analytical methods. The methods address the correct positional coil groupings in the slots to obtain back electromotive forces, mutual and self-inductances, and line currents. These are obtained over a varying load range.
39691
Semidey S. A. et.al
Optimal Electromagnetic-Thermo-Mechanical Integrated Design Candidate Search and Selection for Surface-Mount Permanent-Magnet Machines Considering Load Profiles
IEEE Trans. on Industry Applications, Vol. 47; No. 6; Nov.-Dec. 2011; 2460 – 2468
Most existing design and optimization methods treat the electromagnetic, thermal, and mechanical designs separately. As a result, the effects of power supply, machine control, load profile, thermal effects, and materials are not fully integrated and accounted for, which often leads to over- or underdesign. This paper proposes an innovative and computationally efficient approach which integrates the electromagnetic and thermo-mechanical design for surface mount permanent magnet machines. Particle swarm optimization is part of this integrated process to efficiently find design candidates which optimize certain requirements, such as weight, efficiency, etc. The effects of power supplies, machine controls, load profiles, thermal effects, and materials can thus all be considered systematically in the proposed multiphysics design approach. This results in a multiphysics design tool that can rapidly locate an optimal design candidate for further consideration.
39692
Hsieh, M.-F.
Post-Assembly Magnetization of Rare-Earth Fractional-Slot Surface Permanent-Magnet Machines Using a Two-Shot Method
IEEE Trans. on Industry Applications, Vol. 47; No. 6; Nov.-Dec. 2011; 2478 - 2486
This paper studies the post-assembly magnetization of a fractional-slot, concentrated winding brushless rare-earth surface permanent-magnet machine with six rotor poles and nine stator slots. In the paper, the simulation method is discussed, and it is illustrated that it is possible to fully magnetize the machine after assembly using two pulses of the winding (“two-shot method”) with a rotation of the rotor between pulses. The MMF required for this process is predicted. The method is then validated experimentally using a test motor and a magnetizer. The machine can be magnetized using connection of either two phases or three phases, and both scenarios are investigated. The open-circuit back electromotive forces are obtained to illustrate the partial magnetization after one pulse and full magnetization after two pulses. Load measurements are also carried out. With the increasing use and size of rare-earth magnet machines, the magnetizing procedure is an important aspect of their manufacture; premagnetized assembly can be difficult.
39693
Bangura J. F.
Directly Coupled Electromagnetic Field-Electric Circuit Model for Analysis of a Vector-Controlled Wound Field Brushless Starter Generator
IEEE Trans. on Energy Conversion; Vol.26; No.4; December 2011; 1033-1040
Directly coupled electromagnetic field-electric circuit modeling approach for coupling an electrical machine to its associated external circuit and power electronics has been widely reported in the literature. However, the inclusion of a closed-loop control system, such as conventional vector (field-oriented) control, within a directly coupled electromagnetic field-electric circuit model has not been widely studied. This is partly because it is a rather complex task. This paper introduces a directly coupled electromagnetic field-electric circuit computational model in which a conventional vector control system has been incorporated for detail simulation of vector-controlled electric machinery drive systems. The model has been successfully applied in the design and analysis of a vector-controlled wound field brushless starter-generator system prototype. Comparison between the simulation and test results for both motor and generator modes show excellent correlation that validates the efficacy and computational soundness of the modeling approach.
2.2 Electrical Motors & Drives
39694
Pellegrino G et.al
Design Tradeoffs between Constant Power Speed Range, Uncontrolled Generator Operation, and Rated Current of IPM Motor Drives
IEEE Trans. on Industry Applications, Vol. 47; No.5; Sept.-Oct. 2011; 1995 - 2003
A closed-form approximate formulation is proposed to establish a relationship between the uncontrolled generator (UCG) operation of interior permanent-magnet (IPM) motors at high speed and the constant power speed range (CPSR) and drive current capabilities. High-saliency IPM motors of the PM-assisted synchronous reluctance type are mainly considered in the analysis, since they are proved to have the most favorable ratio between flux weakening capability and UCG voltage. The results of the analysis show the tight relationship between the uncontrolled overvoltage and the CPSR of the drive. Moreover, where the uncontrolled voltage is higher, the relationship between the CPSR and the motor current amplitude becomes stiffer: For small current variations, a large reduction of the speed range can occur. The analysis is validated experimentally on two motors of very different size (500 W and 1 MW).
39695
Chuang Yu & Chau K.T.
Dual-Mode Operation of DC-Excited Memory Motors under Flux Regulation
IEEE Trans. on Industry Applications, Vol. 47; No.5; Sept.-Oct. 2011; 2031 - 2041
The concept of memory is due to the fact that the magnetization level of permanent magnets (PMs) in the motor can be easily regulated by a temporary dc current pulse and then be memorized automatically. By incorporating this concept into the hybrid-field doubly salient PM (DSPM) motor, the resulting dc-excited memory motor can offer effective and efficient air-gap flux control. The purpose of this paper is to newly propose and implement dual-mode operation for the dc-excited memory motor. Namely, by regulating the magnetization level of the PMs, the motor can operate either under the DSPM mode or under the switched reluctance mode while maintaining similar operating performances. Both simulation and experimentation are used to verify the validity of the proposed dual-mode operation.
39696
Tallam R.M.
Integrated Differential-Mode and Common-Mode Filter to Mitigate the Effects of Long Motor Leads on AC Drives
IEEE Trans. on Industry Applications, Vol. 47; No.5; Sept.-Oct. 2011; 2075 - 2083
Pulsewidth-modulated (PWM) ac drives generate high differential-mode (DM) motor voltages due to the reflected wave phenomenon. The common-mode (CM) voltage produced by a PWM inverter also has fast transitions that result in high peak currents to ground. For low-power ac drives, this can present several issues, such as pump-up of the dc bus and failure of the power module due to high instantaneous currents that are often undetected because of the typical sampling algorithm used. In this paper, existing drive output filter solutions are reviewed, and a new filter design is presented, which has integrated DM and CM impedance with damping matched to typical cable surge impedance. This eliminates reflections of both DM and CM traveling waves and also reduces peak cable charging currents. Experimental results are provided to demonstrate that the new filter has improved performance to reduce motor DM and CM voltages and drive output CM current, thus mitigating the issues specifically seen with low-power ac drives. Complete design details for the filter and a particular implementation of the integrated DM and CM reactor are also presented.
39697
Pellegrino G et.al
Unified Direct-Flux Vector Control for AC Motor Drives
IEEE Trans. on Industry Applications, Vol. 47; No.5; Sept.-Oct. 2011; 2093 - 2102
This paper introduces a unified direct-flux vector control scheme that is suitable for sinusoidal ac motor drives. The ac drives considered here are induction motor, synchronous reluctance, and synchronous permanent-magnet (PM) motor drives, including interior and surface-mounted PM types. The proposed controller operates in stator flux coordinates: The stator flux amplitude is directly controlled by the direct voltage component, while the torque is controlled by regulating the quadrature current component. The unified direct-flux control is particularly convenient when flux weakening is required since it easily guarantees maximum torque production under current and voltage limitations. The hardware for control is standard, and the control firmware is the same for all the motors under test with the only exception of the magnetic model used for flux estimation at low speed. Experimental results on four different drives are provided, showing the validity of the proposed unified control approach.
39698
Matsuse K. et.al
Characteristics of Independent Two Induction Motor Drives Fed by a Four-Leg Inverter
IEEE Trans. on Industry Applications, Vol. 47; No.5; Sept.-Oct. 2011; 2125 - 2134
This paper presents the experimental results of the independent drive characteristics of two three-phase induction motors (IMs) fed by a four-leg inverter (FLI). The FLI is a single inverter that can drive two three-phase ac motors independently. The inverter consists of four legs and two capacitors connected in a series. The U and V phases of both motors are connected in each leg, respectively, whereas the W phase of both motors is connected in the neutral point of two-sprit capacitors. The pulsewidth modulation technique in three-phase voltage source inverter is not directly applicable for the FLI because only two phases must be modulated. Then, this paper also analyzes about the neutral point potential of two-sprit capacitors and inverter output voltage. Next, the modulation technique in the FLI is also shown. The experimental results demonstrate the characteristics of two IM independent drives and the validity of those analytic results.
39699
Ewanchuk J.
A Five-/Nine-Level Twelve-Switch Neutral-Point-Clamped Inverter for High-Speed Electric Drives
IEEE Trans. on Industry Applications, Vol. 47; No.5; Sept.-Oct. 2011; 2145 – 2153
A five-/nine-level twelve-switch inverter is described for three-phase high-speed electric machines having a low per-unit leakage reactance. By reducing the voltage blocking requirement of the semiconductors, the neutral-point-clamped (NPC) variant of the coupled inductor (CI) inverter topology (NPC-CI) is more suited to high dc bus voltages than the six-switch alternative (six-switch CI). Operational and design details are described for the NPC-CI inverter using a three-limb inductor core, including practical considerations for the inverter construction and operation, 480 V/208 V inductor mass comparison between six- and twelve-switch topologies, natural voltage balancing of the split-capacitor dc link, and voltage stresses of the freewheel diodes. Improvements in machine performance are illustrated using two experimental test rigs: an unloaded 18 000-r/min 15-hp induction machine to illustrate improved harmonic quality when operating with a limited switching frequency and a high fundamental output frequency, and a loaded 2-hp utility speed induction machine to demonstrate transient performance.
39700
Xiaodong Liang et.al
Influence of Reactors on Input Harmonics of Variable Frequency Drives
IEEE Trans. on Industry Applications, Vol. 47; No.5; Sept.-Oct. 2011; 2195 - 2203
AC line reactors and dc link reactors are widely used in variable frequency drives (VFDs) to improve the drive performance such as reducing input harmonics, improving the input power factor, and protecting the drives from surges, etc. The effectiveness of both types of reactors in reducing input harmonics is affected by many factors, including the loading of the drives and the system source impedance. In this paper, a simulation is conducted to investigate the influence of such factors. Two power distribution systems with VFDs as the dominant loads in the oil field are used as the case studies. The rules to evaluate the needs and effectiveness using ac line or dc link reactors are proposed for practical applications.
39701
Leboeuf N. et.al
Real-Time Detection of Interturn Faults in PM Drives Using Back-EMF Estimation and Residual Analysis
IEEE Trans. on Industry Applications, Vol. 47; No.6; Nov.–Dec. 2011; 2402 - 2412
Interturn stator winding fault is one of the most frequent faults in permanent-magnet synchronous machines (PMSMs). In this paper, we present a new technique for online detection of this fault in PMSMs. It is based on a residual analysis improved by taking into account back-electromotive force waveform estimation, inverter model, and unbalanced inductance matrix. Then, a current residual monitoring block permits to detect the fault and its severity. The simulation and experimental results validate the proposed method and its efficiency.
39702
Darabi A.et.al
Design Optimization of Multistack Coreless Disk-Type Hysteresis Motor
IEEE Trans. on Energy Conversion, Vol.26; No. 4; December 2011; 1081-1087
Coreless dual disks hysteresis motors (CDDHM) have been recently introduced. The CDDHM presents some improvements in power factor and efficiency compared to general hysteresis machines. However, there is not much design or manufacturing experience available and an initial design methodology has not yet been proposed for the new machine. According to this and existing inherent complexity in the model of hysteresis motors, it is difficult to achieve an optimal design solution by applying a conventional optimization method. In this paper, an initial design approach is proposed. Then, a genetic algorithm-based method is developed to find the high-efficiency solution for an optimal CDDHM. The optimized motor has been manufactured and fitted in a test facility with a torque meter. Some experiments are carried out to prove the optimal design. Furthermore, start-up characteristics of the motor are predicted from the model and validated by a routine test.
39703
Cetin, N. O. & Hava A. M.
Compatibility Issues Between the Filter and PWM Unit in Three-Phase AC Motor Drives Utilizing the Pure Sine Filter Configuration
IEEE Trans. on Industry Applications, Vol. 47; No.6; Nov. – Dec. 2011; 2559 - 2569
Inserted between the inverter and the ac motor for the purpose of providing clean sinusoidal voltage at the motor terminals, the pure sine filter (PSF) involves common-mode and differential-mode suppression components. When using PSF in a motor drive and employing advanced pulsewidth modulation (PWM) techniques with discontinuous modulation waveforms, a large common-mode current may circulate through the inverter and the filter resulting in overcurrent stress in the inverter and significant acoustic noise in the filter inductors. This paper first discusses the PSF and advanced PWM techniques, then investigates the performance issues that may arise when combining advanced discontinuous PWM methods with PSF and provides a curement for the overcurrent stress problems by means of a rate of change limiter. The simulations and detailed experimental studies illustrate the inverter overcurrent stress problems and the feasibility of the proposed method to cure the problems. Via experimental performance evaluation of various PWM methods, the paper also suggests, along with PSF, the use of advanced continuous and discontinuous PWM methods with reduced common-mode voltage for the purpose of performance enhancement and filter size reduction.
39704
Das S. et.al
Monitoring of inter-turn insulation failure in induction motor using advanced signal and data processing tools
IEEE Trans. on Dielectrics and Electrical Insulation; Vol.18; No.5; October 2011; 1599 - 1608
Detection of stator winding inter-turn insulation failure at early stages is crucial for promoting safe and economical use of induction motors in industrial applications. Whereas major insulation failures involving larger percentages of winding are easily discernible from magnitude of supply current, minor inter-turn insulation failures involving less than 5% of turns often go undetected. The present contribution reports experimental results of minor faults due to inter-turn insulation failures in stator windings of induction motor under different loading conditions being analyzed using data and signal processing tools combining Park's Transform and Cross Wavelet Transform. Rough Set Theory (RST) based classifier has been used for fault severity monitoring.
3. INSULATION SYSTEM, MATERIALS & INSULATORS
39705
Techaumnat B. & Kadonaga, M.
Electrostatic force behavior of a nonuniformly charged particle on a planar dielectric solid
IEEE Trans. on Dielectrics and Electrical Insulation; Vol.18; No.5; October 2011; 1366 - 1373
This paper presents the analysis of the electrostatic force on a nonuniformly charged dielectric particle resting on a dielectric solid. The purpose of the analysis is to clarify the force enhancement caused by the nonuniform charging when the particle is on the dielectric solid, and to examine the role of the dielectric solid on the force behavior in the presence of an external electric field. The method of images using multipoles is applied to electric field calculation, and the electrostatic force is determined from the Maxwell stress. The analytical results show significant force enhancement due to nonuniform charging even in the case where the particle and the dielectric solid have the same dielectric-constant value. However, with an externally applied electric field, the nonuniform charging also results in higher force magnitude for detachment of the particle from the plane in comparison with the case of uniform charging. The roles of the dielectric constants of the media involved on the electrostatic force behavior are investigated. Critical difficulty for the detachment is not found for a particle with dielectric constant equal to 4, which is remarkably different from the corresponding case of a particle lying on a conducting plane.
39706
Jihuan Tian et.al
Simulation of space charge dynamics in low-density polyethylene under external electric field and injection barrier heights using discontinuous galerkin method
IEEE Trans. on Dielectrics and Electrical Insulation; Vol.18; No.5; October 2011; 1374 – 1382
In this paper, a novel high-order accurate numerical method was proposed to simulate the space charge transport in solid dielectrics. It is based on a unified framework, discontinuous Galerkin (DG) method, to solve both charge concentration and electric field. It is easier to implement and more efficient than the combined DG and boundary element method (BEM) with equivalent numerical accuracy. With this new method and symmetric model parameters for low-density polyethylene (LDPE), space charge concentration and electric field distribution under different external electric field and injection barrier heights were obtained. The simulation shows that above an electric field threshold, large oscillations appear in the time-dependent maximum electric field strength and the total charge quantity. This phenomenon can be considered as a sign of a relatively larger quantity of charge injection compared to the low field regime. When the Schottky injection barrier height in the simulation is raised, this electric field threshold also increases in order to maintain a certain amount of carrier injection.
39707
Cvetic, J. et.al
Extension of lightning corona sheath model during return stroke
IEEE Trans. on Dielectrics and Electrical Insulation; Vol.18; No.5; October 2011; 1383 - 1392
A generalized lightning traveling current source return stroke model has been used to examine the characteristics of the lightning channel corona sheath. A model of lightning channel consisting of a charged corona sheath and a narrow, high conducting central core is assumed. The return stroke process is modeled with the positive charge coming from the channel core discharging the negative leader charge in the corona sheath. According to the corona sheath model proposed earlier by Maslowski and Rakov, it consists of three zones, zone 1 (inner zone containing net positive charge), zone 2 (surrounding zone 1 with negative charge and outer zone 3 without charge. We adopted the assumption of a constant electric field inside zone 1 of the corona sheath proved in the experimental research of the corona discharges in a coaxial geometry of Cooray. This assumption seems to be more realistic than the assumption of a uniform corona space charge density used previously in the study of Maslowski and Rakov, Marjanovic and Cvetic, and Tausanovic et al. Based on the measurements of the electric field performed by Miki et al, the conductivity of the channel sheath in zone 1 is calculated.
39708
Ziari Z. et.al
Simulation of surface potential decay of corona charged polyimide
IEEE Trans. on Dielectrics and Electrical Insulation; Vol.18; No.5; October 2011; 1408 - 1415
Surface potential decay (SPD) of corona charged polyimide (PI) films has been studied using different initial potentials Vo. It has been noticed that the rate of decay increases with initial charging levels. Surface potential profile over the surface of the PI films and return potential generated after charge neutralization have been also experimentally recorded. In order to analyse and explain the decay behavior, the recorded SPD in PI film has been computer simulated using a numerical model based on charge transport by hopping of injected carriers between localized trapping centers. Three parameters (transit time tT, trapping time τT and mean capture time before release τF) controlling the decay kinetic have been estimated by fitting procedure. The effects of the electric field strength on the transport parameters have been also discussed.
39709
Anh T.T et.al
Effect of trapped space charge on mechanical deformation induced by electric field
IEEE Trans. on Dielectrics and Electrical Insulation; Vol.18; No.5; October 2011; 1416 - 1422
An organic insulating film of polyethylene naphthalene 2,6-dicarboxylate (PEN) was characterized by two complementary techniques: the mechanical deformation of the sample surface, induced by the application of an electric field, was obtained by an image correlation technique named DIC (Digital Image Correlation) and the space charge distributions in the thickness direction were measured by FLIMM (Focused Laser Intensity Modulation Method). The validation of the DIC method, which consists of a following of the successive positions of the surface patterns of the sample, is presented. To validate the algorithms and evaluate the performance of the technique, it was applied to computer-simulated speckle images. In a second step, the experimental system was applied to measure the mechanical deformations of a PEN film previously charged by an electric field in order to have space charge accumulation. This space charge accumulation was quantified by FLIMM. The results show that the mechanical behavior of the sample is modified by the presence of space charge.
39710
Tanski M. et.al
Electrohydrodynamic gas pump with both insulated electrodes driven by dielectric barrier discharge
IEEE Trans. on Dielectrics and Electrical Insulation; Vol.18; No.5; October 2011; 1429 - 1432
In this paper, we report the use of a surface dielectric barrier discharge (DBD) for the generation of unidirectional flow inside a glass tube, using external ring electrodes. The electrodes were made of thin metal stripes mounted on the external wall of the glass tube and insulated with resin. One of the electrodes was grounded, the other was connected to an AC power supply. The DBD discharge was generated between the electrodes on the internal wall of the glass tube. As a result, pumping of air through the glass tube occurred. The presented discharge geometry is attractive for electrohydrodynamic (EHD) gas pumping since there is no direct contact between the external discharge electrodes and the pumped medium. The flow rate generated by the EHD pump was calculated using the measured flow velocity maps at the outlet of the pump. The flow velocity maps were obtained using 3D Particle Image Velocimetry (PIV) technique. It was found that the increase in frequency of the ac voltage caused an increase of the flow rate generated by the EHD pump. Accordingly, the increase in the flow rate occurred when the distance between the electrodes had been increased.
39711
Aksamit P. et.al
Electrostatic properties of aged fullerene-doped mineral oil
IEEE Trans. on Dielectrics and Electrical Insulation; Vol.18; No.5; October 2011; 1459 – 1462
In this paper the analysis of the influence of C60 fullerenes on flow electrification of mineral insulating oil during aging is presented. Three sets of samples, one fresh and two aged for 24 h and 96 h were tested for their electrification properties using an improved version of a spinning disk system. The relations between C60 concentration and electrification current were determined for different rotational velocities. It is shown, that C60 may significantly reduce or increase the electrification current in mineral oil, depending on fullerenes concentration. The possible causes of observed behavior are analyzed.
39712
EL-Adawy M.et.al
Numerical simulation of the electrical double layer development: physicochemical model at the solid and dielectric liquid interface for laminar flow electrification phenomenon
IEEE Trans. on Dielectrics and Electrical Insulation; Vol.18; No.5; October 2011; 1463 - 1475
At the solid-liquid interface, a charge zone called the Electrical Double Layer (EDL) appears. It is constituted of two zones of opposite sign, one in the solid and another one in the liquid. When a liquid flows through a pipe, there is a disturbance of the EDL and an axial streaming current is generated. This current is due to the convection of the charges coming from the electrical double layer. In this paper, we present a numerical simulation of the EDL development process in the case of a liquid containing additives or impurities which are partially dissociated into positive and negative ones. We treat the case of laminar flow and an interfacial reaction whose conversion is small compared to the concentration of positive and negative ions in the bulk solution. The boundary conditions are deduced from the kinetics of the wall surface reactions with additives. However, in this paper, the formation of the EDL at the solid-liquid interface is investigated without any flow (static case). Thus, the rate of the wall reaction and the resulting charge concentration in the liquid can be studied. Then, once the equilibrium of physicochemical reaction is reached, convection is forced and the EDL dynamic behavior has been studied (dynamic case). The physicochemical reaction at the solid-liquid interface, the evolution of the space charge density in terms of both the axial coordinates and flow velocity, and the equations of conservation of charge of the liquid species have been implemented to a developed version of "Electricite de France" finite volume CFD tool Code_Saturne, which is designed to solve the Navier- Stokes equations. Finally, the simulation results of the dynamic behavior at different flow rates are compared with the experimental results.
39713
Tanaka T. et.al
Dielectric properties of XLPE/Sio2 nanocomposites based on CIGRE WG D1.24 cooperative test results
IEEE Trans. on Dielectrics and Electrical Insulation; Vol.18; No.5; October 2011; 1482 - 1517
A comprehensive experimental investigation of XLPE and its nanocomposite with fumed silica (SiO2) has been performed by CIGRE Working Group D1.24, in cooperative tests conducted by a number of members; covering materials characterization, real and imaginary permittivity, dc conductivity, space charge formation, dielectric breakdown strength, and partial discharge resistance. The research is unique, since all test samples were prepared by one source, and then evaluated by several expert members and their research organizations. The XLPE used for preparation of the nanocomposites was a standard commercial material used for extruded power cables. The improved XLPE samples, based on nanocomposite formulations with fumed silica, were prepared specifically for this study. Results of the different investigations are summarized in each section; conclusions are given. Overall, several important improvements over unfilled XLPE are confirmed, which augur well for future potential application in the field of extruded HV and EHV cables. Some differences/discrepancies in the data of participants are thought to be the result of instrumental and individual experimental technique differences.
39714
Zhi-Min Dang et.al
Microstructure and dielectric characterization of micro- nanosize co-filled composite films with high dielectric permittivity
IEEE Trans. on Dielectrics and Electrical Insulation; Vol.18; No.5; October 2011; 518 - 1525
Dielectric composite films of the micro-nanosize BaTiO3 (BT) particles embedded into a polyvinylidene fluoride (PVDF) matrix were prepared by using a simple blending and casting processing. Effects of the micro-nanosize cofilled model at different mciro-nanosize volume ratios of BT particles on microstructure and dielectric properties of the composite films were researched. The results show that the nanosize BT particles can be filled into the gaps between the micron-size BT particles so that a tightly stack structure in the BT/PVDF composite film is formed. As a result, the dielectric properties of the composite films with the micro-nanosize BT loading at 40 vol% is higher than these with single nanosize BT loading solely if the interactions between the BT fillers are considered. The maximum values of dielectric permittivity were about 55 because of the superior internal microstructure of composite films when the mciro-nanosize volume ratio of BT particles is close to 1/1. In this case, a remarkable synergistic effect for improving the dielectric properties was also observed. The microstructure and the assumed cofilled model of the composite films would used to explain the experimental results well.
39715
Preetha P. & Thomas M.J.
AC breakdown characteristics of epoxy nanocomposites
IEEE Trans. on Dielectrics and Electrical Insulation; Vol.18; No.5; October 2011; 1526 - 1534
Experiments were conducted to measure the ac breakdown strength of epoxy alumina nanocomposites with different filler loadings of 0.1, 1 and 5 wt%. The experiments were performed as per the ASTM D 149 standard on samples of thickness 0.5 mm, 1 mm and 3 mm in order to study the effect of thickness on the ac breakdown strength of epoxy nanocomposites. In the case of epoxy alumina nanocomposites it was observed that the ac breakdown strength was marginally lower for 0.1 wt% and 1 wt% filler loadings and then increased at 5 wt% filler loading as compared to the unfilled epoxy. The Weibull shape parameter (β) increased with the addition of nanoparticles to epoxy as well as with the increasing sample thickness for all the filler loadings considered. DSC analysis was done to study the material properties at the filler resin interface in order to understand the effect of the filler loading and thereby the influence of the interface on the ac breakdown strength of epoxy nanocomposites. It was also observed that the decrease in ac electric breakdown strength with an increase in sample thickness follows an inverse power-law dependence. In addition, the ac breakdown strength of epoxy silica nanocomposites have also been studied in order to understand the influence of the filler type on the breakdown strength.
39716
Shengtao Li et.al
A new potential barrier model in epoxy resin nanodielectrics
IEEE Trans. on Dielectrics and Electrical Insulation; Vol.18; No.5; October 2011; 1535 - 1543
The dielectric constant and the conductivity of epoxy resin nanocomposites exhibit a lower value at slight filler loading compared with the host epoxy resin. The electrical strength has an increase and presents an optimal value at filler loading of 1 wt%. The interaction zone between the nanoparticles and the polymeric matrix is considered as an independent region. Accordingly, a new potential barrier model is proposed. Based on the model, carriers are restrained in the interaction zone when nanoparticle is in an isolated dispersion, leading to a decrease in both mobility and density of carriers. As a result, the conductivity decrease and the electrical strength increase. The restriction of dipole movement in the interaction zone and the increase of free volume are collectively contributed to the reduction of the dielectric constant. With increasing filler loading, the thickness of the interaction zone extends due to the overlap of the interaction zone, even a conductive path occurs when filler loading exceeds the percolation threshold, leading to a great increase in both mobility and density of carriers. Consequently, the conductivity increase and the electrical strength decrease. The increase of the dielectric constant is chiefly ascribed to the particles.
39717
Nilesh S Phalke & Vivek l. Patil
Novel approaches for low VOC alkyds – key to eco friendly coatings
Paintindia, Vol. LXI; No.11; November 2011; 74-76; 78-80
Alkyd resins have proven themselves both from a cost and performance point of view of coatings applications for architectural metal, wood, industrial and construction equipments. As alkyd paints are solvent-borne, they contribute to Volatile Organic Content (VOC) emissions. Increasing concerns regarding ground level ozone and indoor air quality have spurred research activities to find alternative technologies to lower VOC emissions without compromising performance. This has proven to be a major challenge for the coating industry as the key issue is reformulating solvent home paints having lowest possible VOC while delivering expected performance benchmarks. Designing high solid coatings derived from Hyperbranched polymers, Sucrose Polyesters, DiMethylol Propionic Acid (DMPA) and water Borne Alkyds are a few concepts which can be used for a sustainable and environment friendly coatings without sacrificing the performances.
39718
Pravin G Kadam & Mhaske S.T
Effect of initiator and accelerator concentration on the mechanical properties of cured unsaturated polyester resin
Popular Plastics & Packaging; Vol. LVI; No.10; October 2011; 49-51
Initiator and accelerator are widely used to bring about faster curing of the unsaturated polyester resin. In this study, effect initiator and accelerator is studied on the properties of unsaturated polyester resin. Initiator used is methyl ethyl keton peroxide (MEKP) and accelerator used is cobalt octoate (CoO). Concentration of MEKP is varied from 1% to 3%, and that of CoO from 1% to 3% by weight, strength IS) increases, but at 3% concentration values decreases, as the accelerator concentration increases, TS increases while impact strength and flexural strength decreases.
39719
Darshan Patel & Nidhi Shah
Polymer in Sustainable Energy
Popular Plastics & Packaging; Vol. LVI; No.10; October 2011; 21-24
A transparent solar cell of polymer based solar cell was design and fabricated. The transparent solar cell for window module was composed of a polymeric material PPV )Polyphenylene vinylene), ITO (Indium Tin Oxide) and electrode (Al, mg, Ca). The preparation of the polymeric sheet is by castic process, the electrode is applied by CVD (Chemical Vapor Deposition) process. The solar energy collected by this window can be used to power up small household electrical appliances. As recent development has taken place for polymeric solar cell which is made by a roll-to-roll process that does not involve indium-tin Oxide (ITO). A commercially available kapton (Polimide) foil with an over layer of copper was used as the substrate. Sputtering of titanium metal on to the kapton/copper in a vacuum metalizing process gave the monolithic substrate and back electrode for the devices. The active layer was slot-die coated onto the kapton/Cu/Tifoil followed by slot-die coating of a layer of PET, PC or PEN.
39720
N'Cho J.S. et.al
The gassing tendency of various insulating fluids under electrical discharge
IEEE Trans. on Dielectrics and Electrical Insulation; Vol.18; No.5; October 2011; 1616 - 1625
Since gas evolvement deteriorates the dielectrical properties of insulating fluid, its ability to resist decomposition under electrical discharge is of paramount importance for the safety of power transformers under operating conditions. In this paper, a series of experiments have been performed under electrical discharge according to ASTM D6180. Various insulating fluids were considered. The samples include minerals oils, synthetic and natural esters, and silicone fluid. The results indicate that the gassing tendency of natural esters is much lower than their counterparts. No significant differences between synthetic esters and silicone fluid were observed. Severely hydrotreated and hydrocracked oils indicate a higher gassing tendency. It is also shown that service-aged oil gassing tendency decreases with reclamation passes. The reclamation of service aged oil by three commercially available Fuller's Earth (FE) showed a declined gassing tendency when FE helped reducing the DDF and turbidity. In addition, the theoretical premises that, oil born decay products contribute to the oil gassing, is experimentally confirmed under laboratory conditions. Extended stability test (3 times longer than the standard specification) also provide convincing evidences that each brand of mineral insulating oil might contain a limited amount of unstable hydrocarbons and volatile compounds. This finding indicates that when in service conditions these are gradually decomposed, the gassing tendency should go down.
39721
Ruijin Liao
A comparative study of physicochemical, dielectric and thermal properties of pressboard insulation impregnated with natural ester and mineral oil
IEEE Trans. on Dielectrics and Electrical Insulation; Vol.18; No.5; October 2011; 1626 - 1637
Natural ester is considered to be a substitute of mineral oil in the future. To apply natural ester in large transformers safely, natural ester impregnated solid insulation should be proved to have comparable dielectric strength and thermal stability to mineral oil impregnated solid insulation. This paper mainly focuses on a comparative study of physicochemical, ac breakdown strength and thermal stability behavior of BIOTEMP natural ester/pressboard insulation and Karamay 25# naphthenic mineral oil/pressboard insulation after long term thermal ageing. The physicochemical and dielectric parameters including moisture, acids and the ac breakdown strength of these two oil/pressboard insulation systems at different ageing status were compared. The permittivity and ac breakdown strength of these two oil/pressboard insulation systems at different temperatures were also investigated. And a comparative result of the thermal stability behavior of these two oil/pressboard insulation systems with different ageing status was provided at last. Results show that though natural ester has higher absolute humidity and acidity during the long ageing period, the lower relative humidity of natural ester helps to keep its ac breakdown strength higher than mineral oil. The pressboard aged in natural ester also has higher ac breakdown strength than that aged in mineral oil. The lower relative permittivity ratio of natural ester impregnated paper to natural ester is beneficial to its dielectric strength. Using natural ester in transformer, the resistance to thermal decomposition of the oil/pressboard insulation system could be also effectively improved.
39722
Ilhan S. & Ozdemir A
Effects of corona ring design upon impulse voltage withstand level of 380 kV V-strings
IEEE Trans. on Dielectrics and Electrical Insulation; Vol.18; No.5; October 2011; 1638 - 1646
This study presents the influence of corona rings on impulse withstand performance of 380 kV V-insulator strings. Those strings comprising cap-and-pin type glass insulator units are one of the most common configurations in Turkish National Power Transmission System. Laboratory test setup was constructed for the centre phase of a full scaled tower. Laboratory tests are performed to investigate the lightning and switching impulse performance of the strings equipped with the existing racket type corona rings and the circular type corona rings. Withstand voltages, lower flashover probability levels, flashover routes and times to flashovers are determined under dry and wet test conditions. In addition, some 3D field simulations regarding potential and electric field distributions are also performed for the interpretation of insulator surface flashovers.
39723
Gielniak, J.
Does the degree of cellulose polymerization affect the dielectric response?
IEEE Trans. on Dielectrics and Electrical Insulation; Vol.18; No.5; October 2011; 1647 - 1650
The purpose of this work is to evaluate the influence of the cellulose polymerization degree (DP) on the dielectric response. The research objects were new and aged pressboard samples of the polymerization degree 1435 and 406, respectively. The authors investigated the dielectric response in the time and frequency domains. The research showed that dielectric response characteristics of new and aged samples, of different DP and an identical water content are very close. Their differences are within the limits of statistical dispersion.
39724
Hikita M. et.al
Propagation properties of PD-induced electromagnetic wave in 66 kV GIS model tank with L branch structure
IEEE Trans. on Dielectrics and Electrical Insulation; Vol.18; No.5; October 2011; 1678 - 1685
The authors investigated the effects of a corner that affects the transmission characteristics of a partial discharge (PD) induced electromagnetic (EM) wave, using a gas insulated switchgear (GIS) model with an L-shaped branch. The authors also experimentally investigated the change of amplitude of PD-induced EM wave around the passage of the Lshaped part using a disc-type ultra-high frequency (UHF) sensor located in a 66 kV model GIS. In addition, the effects of transverse electric (TE) mode were examined using a low pass filtering process, and a finite difference time domain (FD-TD) simulation with a simple model was performed. Subsequently, the effects of the L-shaped part that affected the EM wave transmission characteristic were discussed based on a comparison of the results with the analysis. It was found that the effects of the L-shaped part that affected the transmission characteristics of the PD-induced the EM wave did not affect the transverse electromagnetic (TEM) wave mode component, and reflection was generated with a higher frequency component above TE11 mode. It was also shown that the amplitude of the propagating EM wave changed significantly around the L-shaped part due to the superimposition of the reflected TE mode on the latter part of the incoming EM wave.
39725
Ueta G. et.al
Evaluation of breakdown characteristics of CO2 gas for non-standard lightning impulse waveforms - Method for converting non-standard lightning impulse waveforms into standard lightning impulse waveforms
IEEE Trans. on Dielectrics and Electrical Insulation; Vol.18; No.5; October 2011; 1724 - 1733
SF6 gas, an insulation medium used for gas insulated switchgear (GIS), has a high global warming potential, hence an effective alternative means is expected from the environmental perspective. The authors are focusing on CO2 gas, which has a lower global warming potential, as one of its potential alternatives. To use this CO2 gas for the actual GIS, the insulation characteristics for overvoltage waveforms generated in the actual fields (non-standard lightning impulse waveforms) must be obtained. For this purpose, the preceding study experimentally obtained and evaluated the insulation characteristics for various non-standard lightning impulse waveforms covering the surge waveforms generated in the actual field. In the present paper, the experimental results accumulated to date were comprehensively handled to conduct a study on the evaluation method of the insulation characteristics of the CO2 gas gap for non-standard lightning impulse waveforms. Consequently, similarly to the previous study using SF6 gas, the insulation characteristics could be expressed by one characteristic line using the duration as a parameter. Furthermore, after establishing an evaluation method of the insulation specification for generated waveforms based on the characteristic line and applying it to actual surge waveforms at substations as an example, it emerged that the insulation specification could potentially be reduced by about 10%.
39726
Hwu K. I. & Yau, Y. T.
Applying One-Comparator Counter-Based Sampling to Current Sharing Control of Multichannel LED Strings
IEEE Trans. on Industry Applications, Vol. 47; No.6; Nov. – Dec. 2011; 2413 - 2421
In this paper, a fully digitalized current sharing strategy without any analog-to-digital converter (ADC) is presented and applied to light-emitting diode (LED) lighting. By doing so, the cost for digital control is reduced significantly due to no ADC used. Aside from this, LED dimming is easy to realize. Above all, the proposed current sharing method has the capability of resisting variations in input voltage and component parameter. Such a control topology is demonstrated by some experiments and hence is very suitable for LED street lighting.
39727
Hasan, J. & Ang S. S.
A High-Efficiency Digitally Controlled RGB Driver for LED Pixels
IEEE Trans. on Industry Applications, Vol. 47; No.6; Nov. – Dec. 2011; 2422 - 2429
Red–green–blue (RGB) light-emitting diodes (LEDs) are finding widespread use due to recent advances in the LED technology. In this paper, a microcontroller-based RGB driver was designed to drive a 3 $times$ 3 RGB display panel. The proposed driver maintains the minimum drive voltage across the LEDs and current controllers required to keep it in regulation by selecting the minimum drain voltage of the MOSFETs of the current controllers; leading to reduced power dissipation in the MOSFET and increased efficiency in the LED string. The proposed LED driver system is also able to dim each individual LED in the pixel through a dimming controller circuit. Efficiencies of 85%, 90%, and 90% for the red, green, and blue LEDs, respectively, were experimentally verified at the maximum rated current for the RGB driver.
39728
Flores-Garcia E.
Analysis and Design Method for High-Frequency Self-Oscillating Electronic Ballasts
IEEE Trans. on Industry Applications, Vol. 47; No.6; Nov. – Dec. 2011; 2430 - 2436
In this paper, the analysis and design methodology of a high-frequency self-oscillating (SO) electronic ballast with lamp current control are presented. SO electronic ballasts have two important drawbacks: First, the lamp current varies according to the ac input voltage, causing undesired effects in the lamp brightness, and second, the design method lacks precision at very high frequency operation (greater than 200 kHz) mainly due to the $Cgs$ parasitic capacitance. The ballast is modeled by using the descriptive function method and the extended Nyquist criterion; the model of the ballast includes a control circuit and takes into account the high-frequency effect of the MOSFET parasitic capacitance $Cgs$. Finally, experimental results of a 38-W SO electronic ballast prototype with lamp current control for high-intensity discharge lamps are presented to validate the analysis and the proposed methodology. The switching frequency is selected at 2 MHz in order to avoid the acoustic resonance problem.
39729
Nan Chen & Chung, H.S.-H.
Energy-Recyclable Burn-In Technology for Electronic Ballasts
IEEE Trans. on Power Electronics, Vol. 26; No. 9; September 2011; 2550-2562
Eco-friendly electronic products can help save the environment by using less electricity. However, saving energy is not only about reducing the electricity consumption of a product; it should also encompass the electricity consumed in the production of the product. After a product is assembled, it has to go through a burn-in process for weeding out infant mortalities and thus improving the product reliability. The use of energy recycling in the burn-in process is popular nowadays in the power supply industry. However, the development of energy-recyclable burn-in system for electronic ballast manufacturing is less impressive. Existing burn-in process for electronic ballasts is conducted by connecting lamps or resistors at their output. All electrical energy is converted into heat and light. Not only does this method waste electricity, it also raises room temperatures in the factory, requiring additional ventilation systems to release the excessive heat. This paper presents an energy-recyclable burn-in technology for electronic ballast. It can emulate the lamp characteristics from start up to the steady state, process high-frequency ballast output power, and recycle the power back into the grid. An experimental 400-W prototype for high-pressure sodium electronic ballast has been built and evaluated.
39730
Qingcong Hu & Zane R.
Minimizing Required Energy Storage in Off-Line LED Drivers Based on Series-Input Converter Modules
IEEE Trans. on Power Electronics, Vol. 26; No. 10; October 2011; 2887 – 2895
This paper introduces techniques to reduce energy storage in off-line light-emitting diode (LED) drivers. Rather than targeting the ideals of unity input power factor (PF) and constant LED current, a topology is selected to minimize the required energy storage with the more practical targets of 0.9 PF and a selectable LED current ripple. The objectives are accomplished using a combination of the following: first, constant-input-current regulation, which results in 0.9 PF and 34% less required energy storage than when using unity power factor, and is achieved with a simple reference signal that does not require input voltage sensing; second, a two-stage approach that isolates the LED from the capacitor to allow full use of the stored energy; third, a bidirectional second stage (LED string is between the two stages) that processes only the necessary energy storage; and fourth, a selectable regulation band on the LED current ripple to pass through the maximum allowed double-line-frequency ripple. The topology is applied to the series-input modular architecture to utilize low-voltage high-frequency circuits and low-profile components in off-line applications. Experimental results are presented for a series-input system with three modules each driving eight LEDs with 30% double-line-frequency current ripple using small filter capacitors.
39731
Hong S.et.al
Secondary-Side LLC Resonant Controller IC With Dynamic PWM Dimming and Dual-Slope Clock Generator for LED Backlight Units
IEEE Trans. on Power Electronics, Vol. 26; No. 11; November 2011; 3410 - 3422
This paper presents a low-profile low-cost (LLC) resonant controller IC for LED backlight units fully operating at the secondary side. The integrated dimming circuitry is proposed to improve the dynamic current control characteristics and the LED current density for the brightness modulation of a large screen liquid crystal display. A dual-slope clock generator, including a soft start, is proposed in order to overcome the frequency error due to the undershoot found in conventional approaches. In addition, a new dead-time generator is proposed in order to implement an accurate dead time independent of the output frequency of the clock generator. Protection circuits, such as a under voltage lock out, thermal shut down, open LED detector, and shorted LED detector, have been implemented in order to improve the reliability of the controller IC. The chip is fabricated using 0.35 μm bipolar CMOS DMOS decimal technology; the die size is 2 mm × 2 mm. The frequency of the clock generator ranges from 50 to 500 kHz; the dead time ranges from 50 ns to 2.2 μs. The efficiency of the LED driving circuit is 91%. The current consumption of the LLC resonant controller IC is 40 mA for a 100 kHz operation frequency using a 15 V supply voltage.
5. MATERIALS
39732
Nirmalya Dev
Mitigation of marine fouling growth through TBT free antifouling coating – A review
Paintindia, Vol. LXI; No. 11; November 2011; 61-67
Foulings of marine crafts led to the development and widespread use of antifouling paints in the hulls of boars and ships. Fouling costs shipping industry approximately $ 3 billion per annum. Conventional antifouling paints with tributyltin based toxin have served the industry for past 2-3 decades with excellent performance and track record. However antifouling coatings based on organotin compounds possess a world-wide threat to the aquatic environment due to which international Maritime Organization (IMO) have imposed ban on the presence of tin on seagoing vessel effective 2008. This had led to the evolution of several new generation nontoxic environmentally safe antifouling coating systems. Globally researchers and scientists have approached technically in different ways to develop more eco-friendly antifouling coatings. This paper reviews the process of bio-foulings on ships underhull and the categories of different TBT free antifouling-paints.
39733
Aswini K. Mishra et.al
Development of hyperbranched polyurethane coatings: Effect of chain extender and NCO/OH ratio
Paintindia, Vol. LXI; No. 11; November 2011; 53-60
The present work describes the effect of chain extender and NCO/OH ratio on the properties of hyperbranched polyurethaneurea (HBPU-urea) and HB-imide coatings. For this initially, the “CO terminated prepolymer was calculated and completely chain extended by different chain extenders such as 3-aminopropyl triethoxysilane (APTES), pyromelatic dianhydride (PMDA) and N-hydroxy pthallimide (NHTM) to get either the HBPU-urea or HBPU-imide coatings.
39734
Garzon C.et.al
Effect of the Electric Discharge Confinement on the Perforation Density of Porous Materials
IEEE Trans. on Industry Applications, Vol. 47; No.6; Nov. – Dec. 2011; 2367 - 2373
Several methods to enhance the efficiency of paper electroperforation processes are presented in this work. In all the cases, the discharge confinement effect is used for obtaining higher perforation densities than those found in the standard industrial processes. To quantify the efficiency of the proposed methods, statistical tools are used to characterize the 2-D perforation pattern.
39735
Katragadda Gopoichand
Smart Grid – Trends and Bends
Electrical India, Vol.51; No.11; November 2011; 272-273
Smart Grid is grid modernization and effective energy management from generation to consumption. The EPRI definition of Smart Grid states. A Smart Grid is one that incorporates information and communications technology into every aspect of electricity generation, delivery (transmission & distribution) and consumption in order to minimize environmental impact, improve reliability, service efficiency and reduce costs. To the EPRI definition, we would also add asset modernization as an important element of Smart Grid.
39736
Soni Vivek
Energy Security – India’s Demand Supply Position and Sustainable Measures
Electrical India, Vol.51; No.11; November 2011; 260-266
With high economic growth rates and over 15 percent of the world’s population. India is a significant consumer of energy resources. In 2009, India was the fourth larges oil consumer in the world after the United States, Chine, and Japan. Despite the global financial crisis India’s energy demand continues to rise. In terms of end-use, energy demand in the transport sector is expected to be particularly high, as vehicle ownership, particularly of four-wheel vehicles, is forecast to increase rapidly in the years ahead.
39737
Vasudeva P.K.
Nuclear Power in India
Electrical India, Vol.51; No.11; November 2011; 246-255
Nuclear power is the fourth-larges source of electricity in India after thermal, hydroelectric and renewable sources of electricity. As of 2010, India has 20 nuclear reactors in operation in six nuclear power plants, generating 4,780 MW while five other plants are under construction and are expected to generate an additional 2,720 MW. India Nuclear Energy 2011, will provide a global platform for showcasing latest cutting edge nuclear technology and component supplying companies as well as raw material suppliers.
39738
Varma CVJ
Water Resource & Hydropower Development – Global Scenario
Electrical India, Vol.51; No.11; November 2011; 240-244
Fresh water is needed for energy aspect of life from the health of acquatic, ecosystems to human, health, from the need to grow food for the earth’s growing population to the need to provide energy. As the population grows and as the levels of economic development increases, human needs for water will grow. To meet these needs, we already modify all aspects of the hydrologic cycle. We move vast quantities of water from one region to another, build huge reservoirs that store water for dry periods, seed clouds to squeeze more moisture out of them, divert entire rivers from their beds, harness the power of falling water for electricity, pump great quantities of water from ancient underground acquifiers and stop salinity ingress from sea water.
39739
Sahay Kuldeep & Devi Gita
Wind Power Integration effect on power system network and mitigation through STATCOM
Electrical India, Vol.51; No.11; November 2011; 228-233
Nowadays, power systems are facing new challenges, such as increasing penetration of renewable energy sources, growing demands, limited resources, and competitive electricity markets. At present, especially the use of wind power generation connection to distribution systems is increasing at higher rate that ever the impact of wind power generation connection to distribution systems is increasing at higher rate than ever. The impact of wind power integration in the distribution network has been addressed in this article.
39740
Raghunandan S.S
Future of crystalline photovoltaics
Electrical India, Vol.51; No.11; November 2011; 222-224
The crystalline solar is established as a proven, reliable, bankable and profitable solution on harvesting green energy. The global trends on promoting use of clean energy and energy sustainability has lead to the growth of SPV Industry. The discovery of light absorbing photovoltaic materials like silicon. Germanium, Tellurium, Gallium etc., have been found as key raw materials in PV Panel Technology. While few of the Thin film raw materials had very limited supply, manufacturing and efficiency constraints.
39741
Menon Ramanathan
Renewable Energy : A best option to overcome India’s energy crunch
Electrical India, Vol.51; No.11; November 2011; 216-218
Electricity is a most powerful tool for building modern societies and it plays a critical role in eradicating poverty and boosting economies. Yet, according to United Nations’ estimates, 1.5 billion people – nearly a quarter of the world’s population – live without access to reliable power. In the developing world, rolling blackouts are still common, placing citizens and businesses in the dart and off-line for hours. So is the case with India, one of the world’s fastest-growing economies. The country lacks adequate generation capacity and electricity distribution to meets its current needs and support its future growth.
39742
Mathur S.L
Current – sensing techniques for MPPT Solar PV Module
Electrical India, Vol.51; No.11; November 2011; 212-125
Photovoltaic (PV) generation is becoming increasingly important as a renewable source. PV module still have relatively low conversion efficiency, therefore, controlling maximum power point tracking (MPPT) for the solar array is essential in a PV system. Current sensing is one of the most important functions in MPPT. Conventional current sensing method inserts a resister in the path of the current to be sensed. This method incurs significant power loss. Lossless current sensing methods address this issue in DC-DC boost converter by sensing the current without dissipating the power that passive resister do. Five available current sensing techniques are reviewed. Similar to DC-DC boost converter new scheme which uses the inductor property sensing in MPPT is introduced.
39743
Sidhu K.S
Thermal Generation and Environmental Impact
Electrical India, Vol.51; No.11; November 2011; 122-124; 126, 128, 130, 131
India has right from the early days of development depended on coal as a major source of energy in the form of heat or producing power (Electricity). The Thermal Power Stations using coal are contributing to enormous problems of environmental degradation and thereby health hazards. Of the many environmental and public health risks associated with coal, the most serious in terms of its universal and potentially irreversible consequences is global warming. The scientific community has reached an overwhelming consensus that Earth’s climate is warming with potentially devastating future impacts.
39744
Siddhartha Bhatt M
Safety in Coal Fired Thermal Power Station
Electrical India, Vol.51; No.11; November 2011; 112-114, 116, 118, 120
In a thermal power station, safety is to be implemented in four layers starting with the primary operational safety of boilers, turbines, generators, transformers, auxiliaries, switchyard and other major equipment. The primary layer of safety is the control of operational parameters of the major assets within their limits. The next layer is composed of devices (safety valves, circuit breakers, etc.) and schemes (controls, protection etc., will interface to the end devices) on the boiler, turbo-generator transformers, auxiliaries, switchgear etc. The next tier of safety is through the effectiveness of periodic, annual, capital maintenance and renovation and modernization (R&M) which reduces the incidences of accidents. The next level is through surveillance via thermography, remaining life assessment and condition assessment.
39745
Chayanika Saikia et.al
Pollution Control in Thermal Power Plants
Electrical India, Vol.51; No.11; November 2011; 98-100; 102; 104; 106
A thermal power station is a power plant where the prime mover is steam driven. The greatest variation in the design of thermal power stations is due to the different fuel sources. Some thermal power plants also deliver heat energy for industrial purposes, for district heating, or for desalination of water as well as delivering electrical power. In a thermal power plant, the chemical energy stored in fossil fuels such as coal, fuel oil, natural gas is converted successively into thermal energy, mechanical energy and finally electrical energy for continuous use and distribution across a wide geographic area.
39746
Shankar B.G
Overall Power Scenario in India and Efforts to minimize the gap between generation and demand
Electrical India, Vol.51; No.11; November 2011; 90-92; 94; 96
Overall Indian annual energy generation has grown from 515.2 billion units to 811.1 billion units during the years 20001-02 to 2010-11. The average annual generation growth rate was 5.74% but could not meet the demand due to continuous industrial growth, population growth and life style change. The Ministry of Power is planning to cope up with the growing demand but could not reduce the gap between the generation and demand. As fossil fuels are fast depleting, alternate energy sources for clean energy are being explored and developed continuously both in commissioning and R&D to improve efficiency, reduce the cost and payback periods. Different line losses are recorded at different states / areas / towns due to illegal connections, corrupt management, tampering of meters etc. Accurate metering and reducing the losses is very essential to eliminate theft of power to bring the T&D losses to less than 10%.
39747
Pranjal Dutta
Building Efficiency
Electrical India, Vol.51; No.11; November 2011; 78-80; 82; 84; 86
Today buildings worldwide account for upto 40% of total end-use energy. Residential and commercial buildings consume over one-third of all energy and two-thirds of all electricity consumption. Building techniques and materials exist that can dramatically reduce building energy consumption. Unfortunately, most buildings do not take advantage of the significant energy savings available. Because buildings have life spans of 50 to 100 years or more, their poor efficiency has a long – lasting effect on energy needs.
39748
Prashant Kumar Tiwari
Current status and trends of Indian Power Sector
Electrical India, Vol.51; No.11; November 2011; 50-52; 54; 56; 58
India is a fast growing developing economy and has progressed despite the changes on the socio-political front. Power planning will play an important role in the successful power reform. It is essential for India economy growth. Only a financially and commercially sound power sector can attract new investments. India ranks sixth in the world in total energy consumption and needs to accelerate the development of the sector to meet its growth aspirations. The electricity market is undergoing a tremendous transformation not only in India but throughout the world as it moves towards a more competitive environment.
39749
Khan M.A.S.K. & Rahman, M.A.
Implementation of Wavelet-Based Controller for Battery Storage System of Hybrid Electric Vehicles
IEEE Trans. on Industry Applications, Vol. 47; No.5; Sept.-Oct. 2011; 2241 - 2249
This paper presents a wavelet-based multiresolution proportional integral derivative (MRPID) controller for temperature control of the ambient air of battery storage system of the hybrid electric vehicles. In the proposed wavelet MRPID controller, the discrete wavelet transform (DWT) is used to decompose temperature error into frequency components at various resolution of the error signal. The wavelet transformed coefficients are scaled by suitable gains and then added together to generate the control signal of thermal system. The proposed wavelet controller is implemented for battery storage system in both simulation and experiments. The digital signal processor board is used for real-time implementation of the proposed controller. The performance of the proposed wavelet-based MRPID controller is compared with conventional proportional-integral-derivative (PID) and adaptive neural network controllers. The proposed wavelet controller for battery storage system is found more robust and quicker than the conventional and adaptive controllers.
39750
Arritt, R. F. & Dugan, R. C.
Distribution System Analysis and the Future Smart Grid
IEEE Trans. on Industry Applications, Vol. 47; No.6; Nov. – Dec. 2011; 2343 - 2350
The “smart grid” refers to various efforts to modernize the power grid through the application of alternate sources of energy and intelligent devices. The present national interest in smart grid applications has generated many questions concerning the role of distribution engineering in the future. What features do utility engineers need in distribution system analysis tools to support the future smart grid? This paper will discuss some relevant Electric Power Research Institute research in this area that focuses on selected issues related to smart grid analysis relevant to rural utilities. The essential characteristics of distribution system analysis tools to support analysis of these issues are discussed.
39751
Li H. & Pillay P
A Methodology to Design Linear Generators for Energy Conversion of Ambient Vibrations
IEEE Trans. on Industry Applications, Vol. 47; No.6; Nov. – Dec. 2011; 2445 - 2452
An air-cored tubular linear generator is designed and prototyped, to capture transient bridge vibrations to power wireless sensors on a bridge. The relationship between the moving mass, the spring, and the damping for harvesting sufficient vibration energy is developed. The voltage and power of the linear generator with sinusoidal speed are obtained with a transient electromagnetic field analysis. Finally, the ambient experimental results of the linear generator are obtained and analyzed from actual bridge vibrations.
39752
Senturk O. S.
Converter Structure-Based Power Loss and Static Thermal Modeling of The Press-Pack IGBT Three-Level ANPC VSC Applied to Multi-MW Wind Turbines
IEEE Trans. on Industry Applications, Vol. 47; No.6; Nov. – Dec. 2011; 2505 - 2515
Wind turbine converters demand high power density due to nacelle space limitation and high reliability due to high maintenance cost. Depending on the converter structure, the converter thermal performance determines the converter power density and reliability. To estimate the converter thermal performance, the converter structure-based power loss and thermal models are developed in this study for the medium-voltage (MV) three-level active neutral-point-clamped voltage source converter (3L-ANPC-VSC) utilizing 4500 V-1800 A press-pack insulated-gate bipolar transistor-diode pairs and interfacing a 6 MW wind turbine to a MV grid. The switching power loss models are built using the experimental switching power loss data acquired via the double-pulse tests conducted on a full-scale 3L-ANPC-VSC prototype. The converter static thermal model is developed based on the double-sided water-cooled press-pack switches. Via a single-phase test setup with two full-scale 3L-ANPC-VSC legs, the developed power loss and thermal models are validated experimentally. Employing the validated models, the 3L-ANPC-VSC's thermal performance is demonstrated on simulation for a 6 MW wind turbine grid interface. Hence, these converter structure-based models developed and validated in this study are proven to be suitable for the converter power density and reliability studies based on converter thermal performance.
39753
Angquist L.
Open-Loop Control of Modular Multilevel Converters Using Estimation of Stored Energy
IEEE Trans. on Industry Applications, Vol. 47; No.6; Nov. – Dec. 2011; 2516 - 2524
The internal control of a modular multilevel converter aims to equalize and stabilize the submodule capacitor voltages independent of the loading conditions. It has been shown that a submodule selection mechanism, included in the modulator, can provide voltage sharing inside the converter arm. Several procedures for controlling the total stored energy in each converter arm exist. A new approach is described in this paper. It is based on estimation of the stored energy in the arms by combining the converter electromotive force reference, the measured alternating output current, and the known direct voltage. No feedback controllers are used. Experimental verification on a three-phase 10 kVA prototype is presented along with the description of the new procedure.
39754
Takaki K.
Influence of circuit parameter on ozone synthesis using inductive energy storage system pulsed power generator
IEEE Trans. on Dielectrics and Electrical Insulation; Vol.18; No.5; 1752 - 1758
An inductive energy storage system pulsed power generator using semiconductor opening switch (SOS) diodes was employed to drive a co-axial cylinder plasma reactor for ozone synthesis with high yield. Fast recovery diodes were used as SOS diodes in the inductive energy storage system pulsed power generator to produce short-pulse high-voltage with high-repetition rate. The high-voltage pulse was applied to a 1 mm diameter center wire electrode in the reactor. The copper cylinder of 19 mm inner diameter was used as outer electrode and was connected to a ground. Oxygen and dry air were used as source gases and were injected into the plasma reactor with 2 L/min. gas flow rate. The synthesized ozone concentration increased in proportion to pulsed voltages repetition rate under oxygen gas condition. The ozone yield of about 230 g/kWh was obtained in oxygen gas and was independent of circuit parameter. The ozone yield decreased from 230 to 100 g/kWh by changing the source gas from oxygen to dry air. The ozone yield depended on circuit parameters such as capacitance of the primary energy storage capacitor and inductance of the secondary energy storage inductor under dry air condition.
39755
Shukla A.et.al
Hysteresis Modulation of Multilevel Inverters
IEEE Trans. on Power Electronics, Vol.26; No.5; May 2011; 1396 - 1409
The hysteresis modulation for power electronic converters is attractive in many different applications because of its unmatched dynamic response and wide command-tracking bandwidth. Its application and benefits for two-level converters are well understood, but the extension of this strategy to multilevel converters is still under development. This paper summarizes and reviews the various hysteresis modulation approaches available in the literature for multilevel converters. The pros and cons of various techniques are described and compared for tracking the reference signal in order to attain an adequate switching optimization, excellent dynamic responses and high accuracy in steady-state operation. By using the recently developed multilevel hysteresis modulation approaches, the advantages of using several accessible dc potentials in a multilevel inverter have been fully exploited. All of these hysteresis modulation approaches are tested for tracking a current reference when applied to a five-level inverter. The relevant simulation and experimental results are also presented. This study will provide a useful framework and point of reference for the future development of hysteresis modulation for multilevel converters.
39756
Restrepo, J.A
Direct Power Control of a Dual Converter Operating as a Synchronous Rectifier
IEEE Trans. on Power Electronics, Vol.26; No.5; May 2011; 1410 - 1417
This paper presents a dual converter employed as a rectifier with power factor regulation and bidirectional power flow. The active and reactive powers flowing into the converter is controlled using an optimized direct-power-control algorithm. The multilevel structure of the converter is exploited to control the voltage level in each subconverter by selecting the modulation method from one commonly found in the literature, with the option of clamping one of the subconverters. These modulation methods are used to control the power taken by each subconverter, providing limited dc-link voltage regulation. The system is first simulated in SIMULINK, and the results are experimentally validated using a digital-signal-processor-based test rig.
39757
Ruxi Wang
A High Power Density Single-Phase PWM Rectifier With Active Ripple Energy Storage
IEEE Trans. on Power Electronics, Vol.26; No.5; May 2011; 1430 – 1443
It is well known that single-phase pulse width modulation rectifiers have second-order harmonic currents and corresponding ripple voltages on the dc bus. The low-frequency harmonic current is normally filtered using a bulk capacitor in the bus, which results in low power density. However, pursuing high power density in converter design is a very important goal in the aerospace applications. This paper studies methods for reducing the energy storage capacitor for single-phase rectifiers. The minimum ripple energy storage requirement is derived independently of a specific topology. Based on the minimum ripple energy requirement, the feasibility of the active capacitor's reduction schemes is verified. Then, we propose a bidirectional buck-boost converter as the ripple energy storage circuit, which can effectively reduce the energy storage capacitance. The analysis and design are validated by simulation and experimental results.
39758
Mohammadi H.P.& Bina, M.T.
A Transformerless Medium-Voltage STATCOM Topology Based on Extended Modular Multilevel Converters
IEEE Trans. on Power Electronics, Vol.26; No.5; May 2011; 1534 - 1545
A new transformerless four-leg topology is suggested for shunt compensation, the modular multilevel converters (MMC) based on the half-bridge converters, to achieve higher performance as a STATCOM in a distorted and unbalanced medium-voltage large-current (MV-LC) system. Further, an extended MMC (EMMC) is proposed in order to manage more accurate compensation for high-power applications. Both proposals can be controlled for various purposes such as reactive power and unbalance compensation, voltage regulation, and harmonic cancellation. Moreover, related control strategies are also suggested for both the MMC and the EMMC to ensure that the source-end three-phase currents are sinusoidal and balanced. Also, the dc-link capacitors of the half-bridge converters are regulated. One interesting application for the EMMC-based STATCOM could be the improvement in power quality and performance of the electrified railway traction power supply system. Both the MMC- and the EMMC-based STATCOM along with their proposed control strategies were simulated; further, to verify the suggestions, these proposals were also implemented on a 30-kVA modular laboratory prototype. Experiments and simulations confirm the predefined objectives.
39759
Jwu-Sheng Hu et.al
Analytical Solutions of Multilevel Space-Vector PWM for Multiphase Voltage Source Inverters
IEEE Trans. on Power Electronics, Vol.26; No.5; May 2011; 1489 - 1502
This study systematically analyzes multilevel space-vector pulse width modulation for a multiphase voltage source inverter (VSI). The instantaneous output voltages of the VSI, which are called space vectors, can be classified according to the switching states of the VSI. By applying the eigenspace decomposition of the system matrix, the n-phase VSI control problem can be solved analytically. This analysis leads to a switching strategy that uses the fewest space vectors and minimum total conduction time. This yields a minimum switching number and efficient dc supply utilization. Further, the switching strategy of a multilevel multiphase VSI system can be solved based on the switching strategy of a two-level multiphase VSI. Simulations and experimental results confirm the effectiveness of the proposed algorithm.
39760
Hongrae Kim et.al
Inductor Current Measurement and Regulation Using a Single DC Link Current Sensor for Interleaved DC–DC Converters
IEEE Trans. on Power Electronics, Vol.26; No.5; May 2011; 1503 - 1510
Inductor current measurements using only a single dc link current sensor in an interleaved dc-dc converter is introduced in this paper. This technique is appealing for the interleaved dc-dc converter because it minimizes the number of current sensors, thereby reducing sensor cost, weight, and volume. A combination of analytical and experimental results is provided to confirm that the single dc link current sensor technique is capable of achieving attractive performance characteristics in the areas of inductor current reconstruction, inductor current regulation, and output voltage regulation for the interleaved dc-dc converter.
39761
Pengju Kong
Reducing Common-Mode Noise in Two-Switch Forward Converter
IEEE Trans. on Power Electronics, Vol.26; No.5; May 2011; 1522 – 1533
This paper addresses the common-mode (CM) electromagnetic interference noise issues in the two-switch forward converter. The two-switch forward converter has low CM noise compared to other topologies because its symmetric primary-side circuit has two out-of-phase dv/dts that cancel each other. However, parasitic capacitances of the circuit significantly affect the symmetry and degrade the noise reduction. Moreover, the secondary-side circuit of the converter is not symmetric and still contributes to the CM noise. In this paper, the parasitic capacitances of the converter are first modeled. Different transformer structures and their parasitic capacitances are characterized. A general balance technique is introduced to further reduce the CM noise of the converter. For each transformer structure, balance can be achieved with proper connection of the windings terminals and control of the parasitic capacitances to minimize the CM noise of the converter. Experimental results validated the proposed techniques.
39762
Mohammadi H.P.& Bina M.T.
A Transformerless Medium-Voltage STATCOM Topology Based on Extended Modular Multilevel Converters
IEEE Trans. on Power Electronics, Vol.26; No.5; May 2011; 1534 – 1545
A new transformerless four-leg topology is suggested for shunt compensation, the modular multilevel converters (MMC) based on the half-bridge converters, to achieve higher performance as a STATCOM in a distorted and unbalanced medium-voltage large-current (MV-LC) system. Further, an extended MMC (EMMC) is proposed in order to manage more accurate compensation for high-power applications. Both proposals can be controlled for various purposes such as reactive power and unbalance compensation, voltage regulation, and harmonic cancellation. Moreover, related control strategies are also suggested for both the MMC and the EMMC to ensure that the source-end three-phase currents are sinusoidal and balanced. Also, the dc-link capacitors of the half-bridge converters are regulated. One interesting application for the EMMC-based STATCOM could be the improvement in power quality and performance of the electrified railway traction power supply system. Both the MMC- and the EMMC-based STATCOM along with their proposed control strategies were simulated; further, to verify the suggestions, these proposals were also implemented on a 30-kVA modular laboratory prototype. Experiments and simulations confirm the predefined objectives.
39763
Acero J. et.al
Analysis and Modeling of Planar Concentric Windings Forming Adaptable-Diameter Burners for Induction Heating Appliances
IEEE Trans. on Power Electronics, Vol.26; No.5; May 2011; 1546 - 1558
Adaptable-diameter inductors are being implemented in domestic induction hobs in order to increase the range of suitable pot diameters and to achieve the better use of the rated power electronics. Such inductors are arranged by means of several concentric planar windings, usually up to three units, each one of them comprising several litz-wire turns. Currently, one resonant inverter is dedicated to supplying each winding. In this paper, a characterization of these inductors in terms of their impedance matrix is derived. The self-impedance of each winding and those caused by the coupling between them are analyzed. The contribution of this paper lies in the understanding and analysis of the coupling between concentric windings. Unlike transformers, where ideally the magnetic path consists of a lossless material, in domestic induction heating, the vessel is part of the flux path. Consequently, the off-diagonal terms of the impedance matrix have been generalized because they have a resistive component in addition to the classical mutual-inductance component. The analysis presented in this paper also includes the losses in the litz wires generated by the currents in each winding as well as the losses produced by the windings over their concentric neighbors.
39764
Sato, A. & Noguchi T.
Voltage-Source PWM Rectifier–Inverter Based on Direct Power Control and Its Operation Characteristics
IEEE Trans. on Power Electronics, Vol.26; No.5; May 2011; 1559 - 1567
This paper describes a novel control strategy of direct power-control-based voltage-source pulsewidth modulation (PWM) rectifier-inverter. The key of this strategy is direct selection of a switching state of the PWM rectifier-inverter on basis of instantaneous power errors. A relationship between the instantaneous power and the switching state of the PWM rectifier-inverter is theoretically analyzed, which is essential to compose a switching-state table. Effectiveness of the proposed technique is examined through several experimental tests, using a 1.6-kW prototype. As a result, unity power factor operation is achieved by the proposed method, and the output currents are confirmed to be sinusoidal waveforms without large distortion under balanced and unbalanced power-source condition.
39765
Hyun-Lark Do
A Zero – Voltage – Switching DC-DC Converter with high voltage gain.
IEEE Trans. on Power Electronics, Vol.26; No.5; May 2011; 1578 - 1586
A zero-voltage-switching (ZVS) dc-dc converter with high voltage gain is proposed. It consists of a ZVS boost converter stage and a ZVS half-bridge converter stage and two stages are merged into a single stage. The ZVS boost converter stage provides a continuous input current and ZVS operation of the power switches. The ZVS half-bridge converter stage provides a high voltage gain. The principle of operation and system analysis are presented. Theoretical analysis and performance of the proposed converter were verified on a 100 W experimental prototype operating at 108 kHz switching frequency.
39766
Goh Teck Chiang & Itoh, J.I.
DC/DC Boost Converter Functionality in a Three-Phase Indirect Matrix Converter
IEEE Trans. on Power Electronics, Vol.26; No.5; May 2011; 1599 – 1607
An indirect matrix converter (IMC) connected with two input power sources is proposed: a gasoline generator as the main ac power supply and batteries as the secondary power source. The IMC is small in size because of having a dc-link part without an electrolytic capacitor. The dc-link part is utilized by connection with a boost-up chopper with batteries as a secondary input power source. Furthermore, the chopper connects to the neutral point of the motor and utilizes the leakage inductance of the motor as a reactor component. The proposed technique successfully further reduce the size of the converter by removing the boost reactor in the boost converter stage. The proposed converter is simulated and experimentally validated using a 750-W prototype and an induction motor driven with V/f control. The total harmonic distortion of the input and output currents are 4% and 3.7%, respectively, and the efficiency is 96%.
39767
Bo Yuan et.al
A Current-Fed Multiresonant Converter with Low Circulating Energy and Zero-Current Switching for High Step-Up Power Conversion
IEEE Trans. on Power Electronics, Vol.26; No.6; June 2011; 1613 – 1619
A high-efficiency high step-up dc-dc converter is proposed for renewable energy harvesting, where the sustainable power sources, such as PV panels and fuel cells, are characterized by low-voltage high-current output. The proposed converter employs the current-fed half-bridge structure to generate a square-wave current source. Then, a multiresonant tank is used to provide high voltage gain, absorb the parasitic parameters of the transformer, and create zero-current switching (ZCS) condition for all primary switches. By applying a single capacitor instead of LC for the output filter, the maximum voltage of the resonant capacitor is clamped to the output voltage, which reduces the circulating energy within the circuit and offers ZCS to the rectifying diodes. The operation principle is introduced and the steady-state analysis is also carried out for the derivation of the dc voltage gain and the ZCS conditions of the primary switches. The performance of the proposed converter was verified by a 150-W prototype. A peak efficiency of 95.2% was achieved by running the prototype at 255 kHz with 23-V input and 350-V output.
39768
Thurein Paing et.al
Custom IC for Ultralow Power RF Energy Scavenging
IEEE Trans. on Power Electronics, Vol.26; No.6; May 2011; June 2011; 1620 - 1626
This letter presents a custom IC that provides an efficient interface between an ultralow power RF rectifying antenna (rectenna) power source and a microbattery for maximum power scavenging. The energy scavenger IC operates a boost converter in pulsed fixed-frequency discontinuous conduction mode to present a positive resistance to the rectenna. It uses current-starved circuitry, a nonoverlapping gate drive, and a subthreshold current source to achieve a nominal supply current in the 200-nA range for V DD = 2.5 V. Experimental results are given with the IC scavenging energy from a 1.93-GHz patch rectenna to a battery with voltages ranging from 2.5 to 4.15 V. Overall conversion efficiency including all control losses is demonstrated at over 35% at an input power of just 1.5 μW and at over 70% at input power levels over 30 μW. The IC is fabricated in a 5-V, 0.35-μm CMOS process. Although the IC was designed for RF energy scavenging, the low-power boost converter can be applied to other power sources such as wind, vibration, and temperature.
39769
Hongwei Jia et.al
Integration of a Monolithic Buck Converter Power IC and Bondwire Inductors With Ferrite Epoxy Glob Cores
IEEE Trans. on Power Electronics, Vol.26; No.6; May 2011; June 2011; 1627 - 1630
In this letter, we report a concept of integrating a monolithic buck converter power IC with in-package bondwire inductors. The power IC containing all switching devices, driver circuitry, and control logic was designed and fabricated with a standard 0.5-μm CMOS process. Mutliturn bondwires with and without ferrite epoxy glob cores are used as the filter inductor in the buck converter. A prototype system-in-package converter with an output voltage and current of 2.5 V and 120 mA was built to operate at frequencies up to 5 MHz. The power level of the prototype buck converter is scalable by increasing the size of the active power switches.
39770
Govindaraju C.& Baskaran K;
Efficient Sequential Switching Hybrid-Modulation Techniques for Cascaded Multilevel Inverters
IEEE Trans. on Power Electronics, Vol.26; No.6; June 2011; 1639 - 1648
This paper presents four different sequential switching hybrid-modulation strategies and compared for cascaded multilevel inverters. Hybrid-modulation strategies represent combinations of fundamental-frequency modulation and multilevel sinusoidal-modulation (MSPWM) strategies, and are designed for performance of the well-known alternative phase opposition disposition, phase-shifted carrier, carrier-based space-vector modulation, and single-carrier sinusoidal-modulations. The main characteristic of these modulations are the reduction of switching losses with good harmonic performance, balanced power loss dissipation among the devices with in a cell, and among the series-connected cells. MSPWM and its base modulator design are implemented on a TMS320F2407 digital signal processor (DSP). Complex programmable logic device realizes hybrid-modulation algorithm with base pulsewidth modulation (PWM) circulation, and is integrated with DSP for sequential switching hybrid PWM generation. The proposed modulations can be easily extended to three phase, and higher level inverters, operates with same physical structure of the power module. The feasibility of these hybrid modulations are verified through spectral analysis, power loss analysis, simulation, and experimental results.
39771
Huai Wang et.al
A Class of High-Input Low-Output Voltage Single-Step Converters with Low Voltage Stress on the Primary-Side Switches and High Output Current Capacity
IEEE Trans. on Power Electronics, Vol.26; No.6; June 2011; 1659 - 1672
Power conversion from an input voltage of several kilovolts to a low load voltage is of great significance in various applications, but poses serious challenges. In this paper, a new converter, which is able to realize such a large step-down conversion in a single step, is proposed by introducing a novel concept of dc-dc multiphase conversion and n-phase interleaving rectification. The proposed structure is formed by n switch pairs in the primary side, an n-phase isolation transformer with the primary windings connected to dc blocking capacitors, and an n-phase current multiplier in the output side. The switching patterns applied to the switch pairs have a phase difference of 360° mathord/ vphantom 360°n n, and the output inductor currents are interleaved correspondingly, making necessary a smaller output filter. For a Vi input voltage and Io load current, the converter features Vi/n voltage stress on the primary-side switches, and Io/n current stress on the secondary-side inductors and diodes. Thus, the magnetic size of the inductors is considerable reduced. The primary-side switches are commutated with zero-voltage-switching (ZVS). Therefore, rather than using insulated-gate bipolar transistors (IGBTs) or MOSFETs with higher voltage ratings, the most available, notable performing 500/600 V MOSFETs can be used in the proposed converter with several kilovolts supply voltage, allowing for a higher operation frequency and lower conduction losses. Compared with an input-series-output-parallel (ISOP) connection of full-bridge (FB) isolated converters, for the same voltage stress on the switches, the proposed converter requires half of the number of transistors and inherently balances the input voltage among the switch pairs. The switching mechanism of a typical switch pair in the kth interval Ts/n of a switching cycle is analyzed. A d- - c analysis was carried out to determine the dc conversion ratio and the ZVS conditions in an analytical form. It allows for a tradeoff design of the converter, such that to minimize the duty-cycle loss and maximize the ZVS load range. A 1500/48-V, 2-kW prototype with four switch pairs was designed, implemented, and evaluated. The experimental results prove the soft switching of the switches, the low voltage stress across the primary-side switches, and the low current flowing through the rectifier's diodes and inductors. The efficiency measured at nominal power rating was 90.75%.
39772
Huber L.& Jovanović M.M.
Methods of Reducing Audible Noise Caused by Magnetic Components in Variable-Frequency-Controlled Switch-Mode Converters
IEEE Trans. on Power Electronics, Vol.26; No.6; June 2011; 1673 - 1681
Methods and a circuit implementation of audible noise reduction (ANR) in switch-mode converters with variable switching frequency are presented. The audible noise caused by magnetic components is reduced by controlling the switching frequency so that it remains above the audible range as the load decreases. This is accomplished by decreasing the peak value of the main switch current pulses in discrete steps until the peak value of the main switch current pulses is decreased to a level that is sufficiently low not to produce unacceptable audible noise. At very light loads and at no load, the ANR circuit can be disabled in order to meet various worldwide standards that limit the maximum input power. The performance of the proposed circuit was experimentally verified in a 90-W single-stage power-factor-correction flyback adapter.
39773
Yedavalli K.et.al
Simple Control System for a Switcher Locomotive Hybrid Fuel Cell Power System
IEEE Trans. on Industry Applications; Vol. 47; No.6; Nov. – Dec. 2011; 2384-2390
Fuel cells are currently being considered as power sources for vehicles to reduce the need for fossil fuels and reduce greenhouse gas emissions. This paper investigates the use of fuel cells in switcher locomotive applications. To meet the dynamic needs of switcher locomotives, a hybrid system is required that consists of power sources, including ultracapacitors and batteries along with the fuel cell. A simple control algorithm is developed that supplies the demanded power and maintains the proper charge on the battery and ultracapacitor.
39774
Estima, J. O. et.al
A New Approach for Real-Time Multiple Open-Circuit Fault Diagnosis in Voltage-Source Inverters
IEEE Trans. on Industry Applications; Vol. 47; No.6; Nov. – Dec. 2011; 2487 - 2494
Practically all the diagnostic methods for opencircuit faults in voltage-source inverters (VSI) developed during the last decades are focused on the occurrence of single faults and do not have the capability to handle and identify multiple failures. This paper presents a new method for real-time diagnostics of multiple open-circuit faults in VSI feeding ac machines. In contrast with the majority of the methods found in the literature which are based on the motor phase currents average values, the average absolute values are used here as principal quantities to formulate the diagnostic variables. These prove to be more robust against the issue of false alarms, carrying also information about multiple open-circuit failures. Furthermore, by the combination of these variables with the machine phase currents average values, it is possible to obtain characteristic signatures, which allow for the detection and identification of single and multiple open-circuit faults.
39775
He J. & Li Y. W.
Analysis, Design, and Implementation of Virtual Impedance for Power Electronics Interfaced Distributed Generation
IEEE Trans. on Industry Applications; Vol. 47; No.6; Nov. – Dec. 2011; 2525 – 2538
This paper presents a virtual impedance design and implementation approach for power electronics interfaced distributed generation (DG) units. To improve system stability and prevent power couplings, the virtual impedances can be placed between interfacing converter outputs and the main grid. However, optimal design of the impedance value, robust implementation of the virtual impedance, and proper utilization of the virtual impedance for DG performance enhancement are key for the virtual impedance concept. In this paper, flexible small-signal models of microgrids in different operation modes are developed first. Based on the developed microgrid models, the desired DG impedance range is determined considering the stability, transient response, and power flow performance of DG units. A robust virtual impedance implementation method is also presented, which can alleviate voltage distortion problems caused by harmonic loads compared to the effects of physical impedances. Furthermore, an adaptive impedance concept is proposed to further improve power control performances during the transient and grid faults. Simulation and experimental results are provided to validate the impedance design approach, the virtual impedance implementation method, and the proposed adaptive transient impedance control strategies.
39776
Vafakhah B. et.al
Multicarrier Interleaved PWM Strategies for a Five-Level NPC Inverter Using a Three-Phase Coupled Inductor
IEEE Trans. on Industry Applications; Vol. 47; No.6; Nov. – Dec. 2011; 2549 - 2558
Multicarrier interleaved pulsewidth modulation (PWM) techniques are presented for a five-level neutral point clamped inverter using a three-phase coupled inductor. The inverter operation is demonstrated using a simple multicarrier interleaved PWM algorithm. Since both the inverter and inductor power losses are closely linked to the magnitude of the inductor current ripple, improved multilevel interleaved PWM techniques are presented based upon the concept of interchangeability of switching states in each phase. The proposed PWM techniques, which are easier to implement when compared to multilevel space-vector PWM techniques, also exploit the use of switching states with a high-effective winding inductance to minimize the inductor current ripple. Simulation results are presented to illustrate the improvements obtained in the inverter waveforms and their harmonic spectrum. Experimental results demonstrate how the inductor current ripple and the related power losses are significantly reduced using the proposed PWM scheme.
39777
Shukla A.et.al
Natural Balancing of Flying Capacitor Voltages in Multicell Inverter Under PD Carrier-Based PWM
IEEE Trans. on Power Electronics, Vol.26; No.6; June 2011; 1682 - 1693
The flying capacitor multicell inverter (FCMI) possesses natural balancing property. With the phase-shifted carrier-based scheme, natural balancing can be achieved in a straightforward manner. However, to achieve natural balancing with the harmonically optimal phase-disposition (PD) carrier-based scheme, the conventional approaches require (n - 1) × (n - 1) trapezoidal carrier signals for an n-level inverter, which is ( n - 1) × (n - 2) times more than that in the standard PD scheme. This paper proposes two improved natural balancing strategies for FCMI under PD scheme, which use the same (n - 1) carrier signals as used in the standard PD scheme. In the first scheme, the on-line detections are performed of (i) the band in which the modulation signal is located, (ii) corresponding period number of the carrier, and (iii) rising or falling half cycle of the carrier waveform to generate the switching signals based on certain rules. In the second strategy, the output voltage level selection is first processed and the switching signals are then generated according to a rule based on preferential cell selection algorithm. These methods are easy to use and can be simply implemented as compared to the other available methods. Simulation and experimental results are presented for a five-level inverter to verify these proposed schemes.
39778
Wu Chen & Hui S.Y.R.
A Dimmable Light-Emitting Diode (LED) Driver With Mag-Amp Postregulators for Multistring Applications
IEEE Trans. on Power Electronics, Vol.26; No.6; June 2011; 1714 - 1722
Current imbalance should be avoided when multiple LED strings are connected in parallel. In this paper, a dimmable LED driver with magnetic-amplifier postregulators for multistring applications is presented. Powered by a common master source, parallel LED strings are individually regulated by their corresponding adaptive slave sources for current balancing in this proposal. Without linear current regulators, the proposed driver offers relatively high efficiency. Its structure is simpler than multiconverter structures for red, blue, and green LED applications, and is particularly suitable for LEDs with wide parameter variations. The performance of the proposed driver is experimentally verified by a 16.5-W prototype with a load of three 5.5-W LED strings.
39779
Zheng Wang et.al
Hybrid PWM for High-Power Current-Source-Inverter-Fed Drives With Low Switching Frequency
IEEE Trans. on Power Electronics, Vol.26; No.6; June 2011; 1754 - 1764
In this paper, a hybrid pulsewidth modulation (PWM) scheme is proposed to suppress the LC resonance for the high-power current-source inverter (CSI) fed drives with low switching frequency. In CSI drive systems, the selective harmonic elimination (SHE) is selected due to the better performance of harmonics, but the LC resonance cannot be effectively damped due to the lack of control flexibility of SHE. In this paper, SHE is only used for the steady-state operation. The modulation scheme is then switched to space vector modulation with dynamic capacitor voltage control when the transient event occurs. The smoothed transitions between different modulation schemes are proposed. The proposed hybrid method effectively solves the resonant issues in CSI drives, while maintaining the power quality. Both simulation and experiments verify the performance of the proposed hybrid PWM scheme.
39780
Hongyun Huang et.al
A MASH-Controlled Multilevel Power Converter for High-Efficiency RF Transmitters
IEEE Trans. on Power Electronics, Vol.26; No.4; April 2011; 1205 - 1214
Envelope tracking (ET) is one of the most promising transmitter architectures proposed to increase the efficiency of modern wireless communication system. An ET transmitter consists of a linear RF power amplifier and a high-efficiency envelope amplifier, which is always a switched-mode power converter. The envelope amplifier provides a varying drain (collector) bias voltage, which tracks the envelope of the RF input signal, for the RF power amplifier. Thus, the RF power amplifier keeps working in high-efficiency region of most of the time. Therefore, the overall efficiency of the transmitter is increased. This paper proposes a multistage noise-shaping-technique-controlled multilevel power converter to perform as the envelope amplifier in an ET transmitter. Experimental results show that the proposed power converter can reproduce any envelope signals with the maximum spectrum component of 300 kHz and give maximum instantaneous power of 20 W. Compared with pulsewidth modulation, the noise-shaping technique can shape the ripple into noise and the noise will be attenuated by the low-pass filter, which results a better performance, while maintaining high efficiency as well.
39781
Jain A.K. & Ayyanar R.
PWM Control of Dual Active Bridge: Comprehensive Analysis and Experimental Verification
IEEE Trans. on Power Electronics, Vol.26; No.4; April 2011; 1215 - 1227
The dual-active-bridge (DAB) topology is ideally suited for high-power dc-dc conversion, especially when bidirectional power transfer is required. However, it has the drawback of high circulating currents and hard switching at light loads, if wide variation in input and output is expected. To address these issues, this paper presents a comprehensive analysis and experimental results with pulsewidth-modulation (PWM) control of the DAB. The PWM control is in addition to phase-shift modulation between the two H-bridges. The analysis addresses PWM of one bridge at a time and of both bridges simultaneously. In the latter, five distinct modes arise based on the choice of PWM and load condition. The possibilities are analyzed for optimizing power density and efficiency for low-load operation. Finally, a composite scheme combining single and dual PWM is proposed that extends the soft-switching range down to zero-load condition, reduces rms and peak currents, and results in significant size reduction of the transformer. Experimental results are presented with a 10-kW prototype.
39782
Oggier, G.G et.al
Modulation Strategy to Operate the Dual Active Bridge DC–DC Converter Under Soft Switching in the Whole Operating Range
IEEE Trans. on Power Electronics, Vol.26; No.4; April 2011; 1228 - 1236
A new modulation strategy that allows operating the dual active bridge (DAB) dc-dc converter under soft switching in the whole operating range is proposed. This strategy is ruled by imposing a certain modulation index in one of the two bridges and a phase shift between the transformer primary and secondary voltages. Moreover, the proposed algorithm reduces the reactive power and thus reducing the converter conduction losses. An experimental prototype was implemented and some experimental results are presented to validate the theoretical analysis. The experimental results reveal that the overall efficiency of the DAB topology can be improved up to 20% by implementing the proposed modulation strategy instead of the conventional one.
39783
Wensong Yu et.al
High-Efficiency MOSFET Inverter with H6-Type Configuration for Photovoltaic Nonisolated AC-Module Applications
IEEE Trans. on Power Electronics, Vol.26; No.4; April 2011; 1253 - 1260
A novel, high-efficiency inverter using MOSFETs for all active switches is presented for photovoltaic, nonisolated, ac-module applications. The proposed H6-type configuration features high efficiency over a wide load range, low ground leakage current, no need for split capacitors, and low-output ac-current distortion. The detailed power stage operating principles, pulsewidth modulation scheme, associated multilevel bootstrap power supply, and integrated gate drivers for the proposed inverter are described. Experimental results of a 300 W hardware prototype show that not only are MOSFET body diode reverse-recovery and ground leakage current issues alleviated in the proposed inverter, but also that 98.3% maximum efficiency and 98.1% European Union efficiency of the dc-ac power train and the associated driver circuit are achieved.
39784
Effler, S et.al
Efficiency-Based Current Distribution Scheme for Scalable Digital Power Converters
IEEE Trans. on Power Electronics, Vol.26; No.4; April 2011; 1261 – 1269
The trend in next-generation switched-mode power supplies will lead to modular, scalable solutions, which deliver power efficiently over a wide range of operation. This paper details a new approach to introduce more advanced control features to improve system efficiency into these scalable solutions. While these methods have been incorporated into multiphase converters in the past, they all require the distribution of information among the individual converters. An advantage of the proposed method is that it does not require such communication signals between the individual power supplies and is, therefore, fully scalable and cost effective. A system comprising individual, smart converters is proposed, where each converter regulates its respective output power to a level with high efficiency. Converters not required for the delivered output power are shut down. The proposed approach is analyzed theoretically. Implementation details for a field-programmable gate array experimental prototype system are given. The system performance for a four-converter prototype system is analyzed and discussed. The efficiency obtained is compared with the efficiency of a multiphase system with phase-shedding operation and the efficiency of a system with independent power converters without phase-shedding support.
39785
Zhusubaliyev, Z.T.et.al
Torus-Bifurcation Mechanisms in a DC/DC Converter With Pulsewidth-Modulated Control
IEEE Trans. on Power Electronics, Vol.26; No.4; April 2011; 1270 - 1279
Pulse-modulated converter systems play an important role in modern power electronics. However, by virtue of the complex interplay between ordinary (smooth) and so-called border-collision bifurcations generated by the switching dynamics, the changes in behavior that can occur in multilevel converter systems under varying operational conditions still remain to be explored in full. Considering the dynamics of a three-level dc/dc-converter, we demonstrate a number of new scenarios for the birth or destruction of resonant and ergodic tori. One scenario involves the formation of a doubled-layered torus structure around a stable focus point through three subsequent border-collision fold bifurcations. Another scenario replaces one of the fold bifurcations by a global bifurcation. In both of these scenarios, the basic mode of the converter remains stable while other modes grow up and bifurcate around it. We also illustrate the subcritical birth of both an ergodic and a resonance torus from the basic operational mode.
39786
Mingliang Wang et.al
A Surface-Mountable Microfabricated Power Inductor in Silicon for Ultracompact Power Supplies
IEEE Trans. on Power Electronics, Vol.26; No.5; May 2011; 1310 - 1315
A novel silicon-based inductor, power inductor in silicon (PIiS) has been proposed and experimentally demonstrated. The PIiS is fabricated at wafer level using a silicon-molding micromachining technique in which 200-μm-thick copper windings are embedded into a silicon substrate and both sides of the substrate are capped with a polymer-magnetic power composite. Through-silicon vias (TSVs) and copper routings are also added so that a PIiS can be directly used as a surface-mountable packaging substrate. A 3 ×3 ×0.6 mm3 PIiS with a measured inductance of 390 nH has been fabricated. The Q factor of this PIiS is 10 at 6 MHz. An ultracompact buck converter has been made by surface mounting off-shelf power ICs and capacitors on a PIiS. The buck converter is 3 ×3 ×1.2 mm3, which has successfully delivered 500 mA at 1.8 V with an 80% efficiency at 6 MHz.
39787
Zehong Li et.al
A Controllable High-Voltage C-SenseFET by Inserting the Second Gate
IEEE Trans. on Power Electronics, Vol.26; No.5; May 2011; 329 - 1332
A novel high-voltage Controllable SenseFET (C-SenseFET) by inserting the second gate and its conductance model is proposed in this letter. Compared with conventional incontrollable SenseFET, the new structure features a controllable sensing region “S-Region” and a stable charging region “C-Region.” While varying the second gate voltage, the conductance of the channel between the two gates G1 and G2 is altered and the controllability of the on-state current is realized. It is experimentally demonstrated that the values of conductance gD are 100 and 87.5 μS under the second gate biases of 0 and -4 V (with the device width of 75 μm), respectively, which are in agreement with simulations. The charging swing factor of C-SenseFET is measured to be 0.16, only 11% of the conventional counterpart, accomplishing higher stability of charging process. Moreover, the breakdown voltage of C-SenseFET achieves 700 V which increases by 300 V compared with conventional SenseFETs due to the implementation of Double-RESURF.
39788
Hennen, M.D et.al
Single-Phase Switched Reluctance Drive With Saturation-Based Starting Method
IEEE Trans. on Power Electronics, Vol.26; No.5; May 2011; 1337 - 1343
This paper presents the design and an encoder-based starting strategy for a low-cost single-phase switched reluctance machine (SRM). The single-phase SRM cannot produce a continuous torque over one revolution. Therefore, applications that do not require a continuous torque, e.g., pumps and fans, are especially suitable. Another issue of single-phase machines is start up. The starting direction is affected by the initial rotor position. Due to the functional concept of SRM the machine produces no torque at aligned and unaligned position of the rotor and consequently, cannot be started from these positions. To start up from every rotor position a saturation-based starting method is used. The design of the rotor with the saturable area is shown and the principles of an encoder-based starting strategy for a fast start-up under 0.5 s are introduced. Finally, the build prototype and experimental results of the starting strategy are shown.
39789
Xiaofeng Wu et.al
Design, Modeling, and Improvement of Integrated EMI Filter With Flexible Multilayer Foils
IEEE Trans. on Power Electronics, Vol.26; No.5; May 2011; 1344 – 1354
Integrated electromagnetic interference (EMI) filter design method with flexible multilayer (FML) foils is presented. An analysis model for integrated EMI filter with FML foils, distributed electromagnetic component (DEMC) model, is proposed. The DEMC model is verified by the experiment. In addition, method to improve the high-frequency performance of integrated EMI filter is investigated. Prototype of integrated EMI filter with FML foils is made for 1 kW switching power supply. In comparison with the traditional discrete EMI filter, it can reduce total volume by 45%.
39790
Guangyong Zhu et.al
Modeling and Analysis of Coupled Inductors in Power Converters
IEEE Trans. on Power Electronics, Vol.26; No.5; May 2011; 1355 - 1363
This paper describes a new approach to the analysis of switched mode power converters utilizing coupled inductors and presents a novel canonical circuit model for N-winding coupled inductors. Waveform and ripple of the winding current in a coupled inductor converter can be easily determined using the developed model similar to those obtained in an uncoupled inductor converter. Influence of coupling coefficient on converter steady state and transient performance is readily predicted by the proposed model. It is found that in an N-phase coupled inductor converter, the voltage waveforms driving the leakage inductors are no longer the phase node voltages but are the modified voltages with a frequency N times the original switching frequency. In addition, their magnitudes also vary with the coupling coefficient among the coupled windings. Through coupling, a converter is capable of responding faster to load transient depending on the coupling coefficient and control mechanism, and that dependency is analytically revealed in the paper. Finally, a two-phase buck regulator is experimentally tested to verify the proposed model.
39791
Jabbari M.
Unified Analysis of Switched-Resonator Converters
IEEE Trans. on Power Electronics, Vol.26; No.5; May 2011; 1364 - 1376
A mechanism for power processing is presented, in which a certain amount of energy is transferred from the source to the output in each cycle. The result is establishing a family of resonant converters so-called switched-resonator converters. The basic nonisolated formation presented in this paper exhibits a collection of 23 simple dc-dc converters. All topologies are inherently soft switched and systematically synthesized. A plenary analysis of the proposed converters is presented.
39792
Hava A.M. & Cetin N.O
A Generalized Scalar PWM Approach With Easy Implementation Features for Three-Phase, Three-Wire Voltage-Source Inverters
IEEE Trans. on Power Electronics, Vol.26; No.5; May 2011; 1385 - 1395
The generalized scalar pulse width modulation (PWM) approach, which unites the conventional PWM methods and most recently developed reduced common mode voltage PWM methods under one umbrella, is established. Through a detailed example, the procedure to generate the pulse patterns of these PWM methods via the generalized scalar PWM approach is illustrated. With this approach, it becomes an easy task to program the pulse patterns of various high performance PWM methods and benefit from their performance in modern three-phase, three-wire voltage-source inverters for applications such as motor drives, PWM rectifiers, and active filters. The theory is verified by laboratory experiments. Easy and successful implementation of various high-performance PWM methods is illustrated for a motor drive.
39793
Oswald N. et.al
Analysis of Shaped Pulse Transitions in Power Electronic Switching Waveforms for Reduced EMI Generation
IEEE Trans. on Industry Applications, Vol. 47; No.5; Sept.-Oct. 2011; 2154 - 2165
Consideration of the higher order time derivatives of voltage and current transitions in power semiconductor devices enables the specification of “S-shaped” switching waveforms which offer an improved tradeoff between high-frequency EMI generation and switching losses. In comparison with the widely used first-order derivative trapezoidal switching waveform approximation, Fourier analysis of the proposed “S-shaped” waveform shows that it exhibits a 20 dB/dec steeper spectral gradient at high frequencies, resulting in a 20 dB greater reduction in high-frequency spectral content per decade increase in rise time. Numerical analysis of the proposed waveform shows that both peak and total RF power, employed as indicative EMI metrics, are reduced significantly with no increase in overall switching time. Experimental investigation of the effect of introducing a frequency-selective EMI transmission path shows that the overall trends in the relationships between time-domain waveform parameters and high-frequency spectral content are maintained, while the values of the waveform timing parameters which minimize the two EMI metrics are changed.
39794
Bragard M.
The Integrated Emitter Turn-Off Thyristor (IETO)—An Innovative Thyristor-Based High Power Semiconductor Device Using MOS Assisted Turn-Off
IEEE Trans. on Industry Applications, Vol. 47; No.5; Sept.-Oct. 2011; 2175 - 2182
This paper focuses on a new realization method of an emitter turn-off thyristor (ETO). The low-inductive requirements for the unity gain turn-off capability of a gate commutated thyristor (GCT) led to bulky driver stages directly attached to the device. This, combined with the need for electrolytic capacitors, inherently leads to mechanical and thermal design problems, which significantly limit the application opportunities, as well as the device's lifetime and reliability. The concept of the ETO overcomes the need for a capacitor bank by using MOSFETs in the cathode current path of the thyristor. The thermal limitations of the gate driver unit are attenuated by this concept, its bulky lay-out is not. The approach presented in this paper overcomes some drawbacks of the known ETO by integrating the MOSFETs into the press pack. Hereby, a significantly smaller and less complex driver design is achieved.
8. POWER SYSTEM
39795
Nitin Sikri
A Paradigm Shift – Time to break the shackles of conventional DC power technologies
Electrical India, Vol.51; No.11; November 2011;194-197
Most of the utilities are transforming their operations and equipment, both Electrical and transmission however the adoption of new DC Power System technologies are yet to find their place in India barring few. Enter any power utility site and you will come across bulky and highly and highly conventional battery charger systems, which supply DC power to mission critical equipment. There are thyristor-based
DC Power Systems (DCPS).
39796
.Hirose H. & Zaman F.
More accurate diagnosis in electric power apparatus conditions using ensemble classification methods
IEEE Trans. on Dielectrics and Electrical Insulation; Vol.18; No.5; October 2011; 1584 - 1590
Recently, the classification study is accelerated, especially in machine learning expertise. Although the decision tree was still recommended as a classification tool in diagnosing electric power apparatus because of the property having the visible if-then rule, the recent development in classification methods, especially those using the ensemble methods, suggests us to apply these methods to condition diagnosis area. In this paper, we report that the new ensemble methods show extremely high accuracy in classification of the electric power apparatus diagnosis, although rule visibility is sacrificed.
9. POWER TRANSMISSION & DISTRIBUTION
39797
Gurudeo Sinha
Threat of mounting financial losses in Electricity Distribution on Indian economy and way forward
Electrical India, Vol.51; No.11; November 2011; 166-168; 170
The Electricity Act, 2003 envisaged a new era in the power sector with unshackling of the sector from government controls, establishment of independent regulator institutions, delicensing of thermal generation and establishment of unbundled power generating, transmission and distribution companies operating on commercial principles for making available good quality power to all. Competition was to be the cornerstone for bringing in operational efficiency and it was considered that competition will determine the price rather than any cost plus exercise on the basis of operating norms and parameters. But this was a dream too utopian to come true.
39798
de Pereira, C.E.M. & Zanetta, L.C.
Fault Location in Multitapped Transmission Lines Using Unsynchronized Data and Superposition Theorem
IEEE Trans. on Power Delivery; Vol. 26; No.4; October 2011; 2081-2089
Lines with several taps are frequent and involve a large number of small towns and customers. With the need for costs reduction, this solution has been adopted in Brazilian utilities, with measurements only at the two terminal substations of the main line. The relevance of the problem is related to the long time for fault location when there are several secondary tap lines, depriving a large number of customers of energy during this period. Since there is not yet an adequate approach for this configuration, without additional hardware and measurements in tap lines, this paper presents a low-cost solution focusing on the synchronization of data measurements and the fault location in the main line or in the tap lines. The algorithm can handle the critical condition of zero-sequence infeed of star-delta transformers connected to tap lines, detecting the faulty section through the superposition theorem and finally obtaining the fault distance. Simple and accurate enough expressions were developed for fault location in order to help computer implementation of the algorithm. The algorithm also enables fault location in double-circuit main lines with several tap lines. The results, considering various line configurations and fault types, are presented, showing the accuracy and efficiency of the proposed method.
39799
Sanaye-Pasand M. & Jafarian P.
An Adaptive Decision Logic to Enhance Distance Protection of Transmission Lines
IEEE Trans. on Power Delivery; Vol. 26; No.4; October 2011; 2134 - 2144
This paper introduces adaptive decision-making logic to improve the performance of distance protection of transmission lines. The proposed approach incorporates the trajectory of the measured impedance into the relay final decision-making logic through a weighting procedure. Two criteria are used to weigh the impedance plane appropriately, where higher weights are assigned to the faults occurring at the interior areas of the relay protective zone and low resistance faults. The weights assigned to impedance samples are added together considering the amount of smoothness of the measured impedance trajectory. An adaptive neurofuzzy inference system (ANFIS) is used to implement the proposed decision logic. Meanwhile, the fault current amplitude is considered as the other input of the ANFIS network to accelerate the relay operation for close-in faults and to incorporate an index for the source-to-line impedance ratio into the final decision-making logic. Extensive simulation studies using PSCAD/EMTDC software indicate that the proposed approach provides a very reliable technique to make the distance protective scheme faster and smarter. It helps to achieve the optimal compromise between the protective relay operation time and security.
39800
Nouri H. & Alamuti M.M.
Comprehensive Distribution Network Fault Location Using the Distributed Parameter Model
IEEE Trans. on Power Delivery; Vol. 26; No.4; October 2011; 2154 - 2162
A typical low- or medium-voltage distribution feeder consists of numerous branches as well as laterals and heterogenic conductor lines. The lack of measurement points and the presence of unbalanced loads make it more complicated for the construction of fault-location algorithms. In this paper, a brief and comprehensive review is presented which introduces and compares published papers in this area to date. In addition, the authors have devised a single-end fault-location algorithm using the distributed parameter model to overcome all of the aforementioned limitations in distribution feeders. The validity of the devised algorithm is studied within the PSCAD-EMTDC environment. This model provides more accurate results as the distributed nature of losses and capacitive effects are considered whereas in the available algorithms, these are ignored. A comparison which is made between the proposed method and two of the most complete available algorithms shows the superiority of our algorithm. Also, the proposed algorithm is able to locate various fault types in the network that has different phase laterals unbalanced loads and heterogeneity of the feeder line.
10. PROTECTION & PROTECTIVE DEVICES
39801
Homce, G. T. & Cawley J. C.
Understanding and Quantifying Arc Flash Hazards in the Mining Industry
IEEE Trans. on Industry Applications, Vol. 47; No.6; Nov. – Dec. 2011; 2437 - 2444
Arc flash generally refers to the dangerous exposure to thermal energy released by an arcing fault on an electrical power system, and in recent years, arc flash hazards have become a prominent safety issue in many industries. This problem, however, has not been effectively addressed in the mining industry. Mine Safety and Health Administration (MSHA) data for the period 1990 through 2001 attribute 836 injuries to “noncontact electric arc burns,” making them the most common cause of electrical injury in mining. This paper presents results from several elements of a recent National Institute for Occupational Safety and Health study of arc flash hazards in mining and provides information and recommendations that can help reduce these injuries. The characteristics of past arc flash injuries in mining are first outlined, such as the electrical components and work activities involved (based on MSHA data). This is followed by a review of important concepts and terminology needed to understand this hazard. Next, methods for identifying, measuring, and managing arc flash hazards on a power system are covered, with emphasis on recommendations found in NFPA 70E, Standard for Electrical Safety in the Workplace. Finally, results are presented from a detailed arc flash hazard analysis performed on a sample mine electrical power system using IEEE 1584-2004a, focusing on components and locations presenting severe hazards, as well as engineering solutions for reducing the risk to personnel.
39802
Ning Du et.al
Phenomena and Mechanism Analysis on Overvoltages Caused by 40.5-kV Vacuum Circuit Breakers Switching Off Shunt Reactors
IEEE Trans. on Power Delivery; Vol. 26; No.4; October 2011; 2102 – 2110
In view of frequent and severe overvoltage failures of 40.5-kV vacuum circuit breakers (CBs) while switching off the shunt reactors in the 35-kV distribution systems in China, a series of field tests was carried out to determine the mechanism of this kind of disruption. The transient process and phenomena were analyzed and summarized based on the overvoltage waveforms obtained from the field tests. The experimental results indicated that the probability of reignition is greater for a 40.5-kV CB than in a 12 kV one. The interphase overvoltage was especially critical. The causes of severe overvoltages were analyzed, and it was indicated that the difference of CBs, multireignitions by the interphase coupling, and the different application conditions were the main effect factors. In addition, some suggestions were given.
39803
Yucheng Zhang & Dougal, R.A.
Soft-Synchronization of Generators Using Controllable Inductive Fault Current Limiters
IEEE Trans. on Power Delivery; Vol. 26; No.4; October 2011; 2428 - 2435
We describe a method for soft-synchronization of generators by controlling an inductive fault current limiter located between the generator and the grid. Our method limits the peak shaft torque and the frequency oscillations that normally occur following mistimed closure of the bus tie switch. The method improves the success rate of generator close-in, especially during emergencies or when operating with low transient-stability margin, with low inertia and, therefore, it lengthens the life of turbogenerators. This method introduces no adverse effects during an ideal (correctly timed) generator-synchronization process. We prove the success of the technique by using transient time-domain analysis and describe the control and an approach to analyze the soft-synchronization process that can be generally applied to either an infinite power system or to a limited-capacity system. After the generator is synchronized to a grid and operates stably, the transient-stability margin between the generator and the grid is not affected by this method. This soft-synchronization method has been validated by simulations with the increased critical margin of the rotor-angle difference and the improved faulty synchronization process with limited power impulse and frequency oscillation.
39804
Jafari, M. et.al
Voltage Sag Compensation of Point of Common Coupling (PCC) Using Fault Current Limiter
IEEE Trans. on Power Delivery; Vol. 26; No.4; October 2011; 2638 - 2646
In this paper, voltage sag compensation of point of common coupling (PCC) using a new structure of fault current limiter (FCL) is proposed. The proposed structure prevents voltage sag and phase-angle jump of the substation PCC after fault occurrence. This structure has a simple control method. Using the semiconductor switch (insulated-gate bipolar transistor or gate turnoff thyristor at dc current rout leads to fast operation of the proposed FCL and, consequently, dc reactor value is reduced. On the other hand, the proposed structure reduces the total harmonic distortion on load voltage and it has low ac losses in normal operation. As a result, other feeders, which are connected to the substation PCC, will have good power quality. Analytical analysis and simulation results using PSCAD/EMTDC software and experimental results are presented to validate the effectiveness of this structure.
39805
Frost & Sullivan’s
The Indian Low and Medium Voltage Switchgear Market – Gearing for an Upsurge
Electrical India, Vol.51; No.11; November 2011; 190-193
Increasing investments are being witnessed in the industrial segment, especially with respect to city and rural infrastructure development programs and establishment of commercial and residential corridors across India. The Government of India and Ministry of Power are thus planning extensive power augmentation and improvement of electrical networks to support this growth. The need to have a safe, reliable, and efficient power distribution setup at both macro and micro levels is providing growth opportunities for the switchgear markets in India.
39806
G.R. Patel
Advances in Switchgear Technologies
Electrical India, Vol.51; No.11; November 2011; 186-189
India has plans to provide electricity to every household and industry under mission 2012, ‘Power to All’. As a part of this, a T&D network expansion has been planned in a big way over and above generation. Voltages as high as 800 kV are being used for transmission of bulk power at present. 1200 kV voltage experimental station is being set up to gather data for the future 1200 kV systems.
39807
Tsuboi T et.al
Insulation breakdown characteristics of UHV-class gas insulated switchgear for lightning impulse withstand voltage test waveform - K-factor value and front time related characteristics
IEEE Trans. on Dielectrics and Electrical Insulation; Vol.18; No.5; October 2011; 1734 - 1742
The lightning impulse withstand voltage test waveform for electric power equipment is specified in IEC 60060-1 "High-voltage test techniques" as revised in 2010. At present, test standards for UHV-class equipment are under study. Increasing equipment capacity and the digitization of measuring equipment are mentioned as these backgrounds. Withstand voltage test by the standard waveform specified in the previous standard had been difficult (it eventually becomes an overshoot waveform) with increasing equipment capacitance. In response, an evaluation method using the kfactor function (test voltage function) was introduced, whereby the overshoot waveform was converted to the test voltage waveform. To date, concerning these kfactor values, measurement results based on experiments have been reported, but most were from small-scale insulation models with breakdown voltage levels mainly around 100 kV. The present study reports the experimental results of the insulation breakdown characteristics for the lightning impulse withstand voltage test waveform in the largest SF6 gas insulation model possible assuming actual UHV-class gas insulated switchgear. Breakdown voltage and breakdown time were measured with the superimposed oscillation frequency, overshoot rate, and front time as parameters. Following evaluation of the k-factor value based on these experimental results, the k-factor value with the overshoot rate of 10% was almost identical to that of the existing k-factor function. Consequently, evaluation using the existing k-factor function is considered appropriate. Subsequently, the existing k-factor function is most likely to be effective also for UHV-class equipment. In addition, it emerged that changes in the insulation breakdown characteristics due to the extension of the front time were small. It was considered that extending the front time, rather than allowing an excessive overshoot rate, would enable proper verification of the insulation performance as part of standard assuming UHV-class equipment.
39808
Arshad M. & Islam, S.M.
Significance of cellulose power transformer condition assessment
IEEE Trans. on Dielectrics and Electrical Insulation; Vol.18; No.5; October 2011; 1591 – 1598
Power transformers are designed to withstand system abnormalities such as over voltages and external short-circuits. Transformer monitoring and diagnostics are the effective techniques in preventing the eventual failures and contribute to ensure the plant's reliability. Transformer life mainly depends on the integrity of its solid insulation (cellulose). The solid insulation in transformers degrades with time at rates which depend on the temperature and the amount of moisture, oxygen and acids in the insulation system. Moisture and oxygen cause the paper insulation to decay much faster than normal. Moisture in a transformer accelerates the aging process and causes severe deterioration in the mechanical and electrical properties of insulation system. The aging of paper insulation is irreversible. The degree of polymerization value is a main relation between insulation deterioration and formation of aging products. To predict a failure or an unusual behavior, an accurate interpretation of monitoring, diagnostics and maintenance data is required. The monitoring of insulation system and verification of core and winding mechanical integrity allow optimization of the lifecycle management of an asset. This paper presents an investigation and condition assessment of 152 MVA, 512 kV, 1-phase, 2-winding generator step-up transformer having a history of combustible gases.
39809
Ueta G. & Wada, H.
Partial discharge signal propagation characteristics inside the winding of gas-filled power transformer - study using the equivalent circuit of the winding model
IEEE Trans. on Dielectrics and Electrical Insulation; Vol.18; No.5; October 2011; 1668 - 1677
The soundness of a gas-filled power transformer under an operating voltage is evaluated in partial discharge (PD) test of long-duration ac withstand voltage test. To establish clear control criteria for this PD test, the authors initially conducted a study on the harmful PD level of materials themselves used in a gas-filled transformer. In the actual PD test, since the PD having occurred inside the transformer is measured from the outside, the measured signal is damped due to various influential factors. Since this damping must be taken into consideration to establish control criteria, a preceding study investigated the propagation characteristics of PD signals through actual measurement using transformer winding models. As a result, it was found that the PD having occurred inside the winding is detected as the signal significantly damped depending on the position of occurrence. This paper studies whether PD signal propagation characteristics can be analytically evaluated using the equivalent circuit of the transformer winding. This analytical evaluation, if feasible, can be applied to various winding structures and will make it possible to evaluate the propagation characteristics in further detail as well as the validity of the actual measurement results. The study was conducted on the interleaved and continuous disk windings to make a comparison between the analysis and measurement results of the voltage waveform and the propagation pattern at various locations inside the winding with the position of occurrence and measurement position of the PD as parameters. Consequently, it emerged that the analysis using the equivalent circuit could adequately simulate the propagation pattern and waveform shape of the PD signal. A detailed study using this equivalent circuit also clarified the fact that the PD signal propagation waveform was determined by the winding constant and the terminal conditions. Furthermore, the analytical and measurement results of the transmission r- - ate were almost identical, whereby it was analytically confirmed that the transmission rate significantly decreased depending on the position of occurrence of the PD. It also emerged that, since the frequency characteristics of the PD measurement device may influence the transmission rate, the PD control criteria must be studied taking such influence into consideration.
12. TESTING
39810
Nath S.K & Narayana B.H
Ultrasonic Non-Destructive Evaluation (NDE) based internal inspection of pressure vessels for better maintenance practice
Journal of Non destructive Testing & Evaluation, Vol.10; No.2; September 2011; 65-67
This paper discusses about the possibility of detection of entrapped foreign object in a pressure vessel by ultrasonic inspection technique. The inspection plan is designed and illustrated here. Successful in-situ implementation of this technique will help in achieving better maintenance practice for the plant components.
39811
Veeraraghavan Sundararaghavan & Krishna Balasubramaniam
On the conversion of multi-frequency “apparent” conductivity data to actual conductivity gradients on peened samples.
Journal of Non destructive Testing & Evaluation, Vol.10; No.2; September 2011; 57-64
This paper addresses the interpretation of “apparent” conductivity measurements as a function of frequency in order to determine the actual conductivity profile as a function of depth in a conducting material. Simulation “apparent” conductivities are not indicative of actual conductivity gradients because of inherent constant conductivity approximation that is assumed at every frequency. This paper focuses on facilitating the conversion of the multi-frequency “apparent” conductivity data conductivity depth profiles through a Model based inversion scheme. The inversion uses a multi-layer axi-symmetric finite element model as the forward model and uses an optimal skin depth approximation for isolating the integral effects of the conductivity gradients on the multi-frequency “apparent” conductivity measurements. Unlike the inductions inversion method that has been reported elsewhere, this method does not depend on the sensor coil parameters and is robust enough to accommodate for common measurement uncertainties. Also, commercial multi-frequency measurements instruments can be used to obtain input data for the inverse model. Possible application of the model towards characterization of residual stresses in peened specimens is also addressed.
39812
Ramakrishna R et.al
NDE Technique for Reactor Core Vibration Measurement in FBRs
Journal of Non destructive Testing & Evaluation, Vol.10; No.2; September 2011; 53-56
The prototype Fast Breeder Reactor (PFBR) which is under construction at Kalpakkam, India, is a 500 MWe sodium cooled pool type reactor. The core of the PFBR consists of 1758 free standing subassemblies, out of which 181 are fuel subassemblies, supported on the grid plate. Coolant sodium flows axially from the bottom of the subassembly to top and it is in turbulent regime, which can excite flow induced vibration (FIV) of fuel subassemblies. Flow induced vibration is not desirable as it can cause failure of the fuel element clad tubes from fatigue, wear and vibration induced fretting. Excessive vibration can also cause reactivity fluctuations, rattling and power control problems. During commissioning of PFBR, it is planned to measure the subassembly vibration in sodium at isothermal condition at 200oC.
39813
Sony Punnose et.al
Non destructive detection of debonding in adhesively bonded metal / ceramic composite plates
Journal of Non destructive Testing & Evaluation, Vol.10; No.2; September 2011; 47-52
Studies have been carried out for detecting the debonding in ceramic-metal composite laminates of Zirconia Toughened Alumina bonded to Titanium alloy (ZTA/Ti) plate. Composite panels of ZTA/Ti with simulated debonds have been tested to assess the feasibility of thermography as a non destructive testing method for detection of debonds. The method has been studied vis-à-vis ultrasonic technique. Pulse phase and lockin thermography techniques have been used for detection of debonds. The thermogram clearly reveals the debonding as well as the non-uniformity in bonding. Ultrasonic attenuation drop has been measured to detect the debonding in the specimens. The study shows that both thermography and ultrasonic techniques can be adopted for detecting the debonding in the composite plates.
39814
Ponnayira Sundaravel S & Kannan S
Power factor and Power measurement using ordinary CRO
Journal of Non destructive Testing & Evaluation, Vol.10; No.2; September 2011; 174-181
The Power Factor (PF) of a load such as tube light, fan, 3 - f motor, water heater can be measured by using analog PF meter; a digital PF meter (micro-controller based); by using an experimental set-up (voltmeter ammeter and wattmeter) and using a PF transducer. In a laboratory or electronic work-shop, the PF of a load can be measured using a two channel cathode ray oscilloscope (CRO). The measurement of PF of a load either 1-f or star/delta connected 3 - f (lagging or leading in nature) using the CRO, is proposed. This method uses potential transformer (PT) and current transformer (CTJ) for voltage and current measurement. The importance of Isolation Transformer to protect the CRO during measurement is also discussed.
39815
Petre Minciunescu & Gabriel Antonesei
Novel Harmonic Analysis Method Improves Accuracy, Reduces Computation Overhead in Smart Meters
Journal of Non destructive Testing & Evaluation, Vol.10; No.2; September 2011; 160-162; 164
With wider deployments of smart meters, smart grids, and distributed generation, power quality monitoring has become increasingly important. Harmonic analysis of current and voltage signals allows energy meters to characterize key power quality indicators, including the state of the load or supply, enabling predictive maintenance or system optimization.
13. TRANSFORMERS
39816
Jean – Claude Duart & Thomas Lim
New Developments in Power Transformers for Large Wind Turbines
Electrical India, Vol.51; No.11; November 2011; 140-142,144
In recent years, the average capacity of wind turbines installed have increased due to derived generation and space efficiency from the large capacity wind turbines. Important challenges are expected from the development of the new and larger with turbines as when the capacity increases the complexity of the technology, handling, installation, operation and maintenance increases exponentially. Reliability and safety of the equipment represents the critical parameters in the choice of the components. This article will focus on the developments of one of the electrical components. This article will focus on the developments of one of the electrical components, the step up distribution transformers that connect the turbine to the grid. Two main technologies exist for those transformers and this article will highlight it.
39817
Behjat V.et.al
Diagnosing Shorted Turns on the Windings of Power Transformers Based Upon Online FRA Using Capacitive and Inductive Couplings
IEEE Trans. on Power Delivery, Vol. 26; No.4; October 2011; 2123 - 2133
Interturn faults are a significant problem in power transformers that can eventually burgeon into catastrophic faults and likely result in an overall network failure. The main problem with SFRA as one of the well-recognized diagnostic tools for detecting winding faults is its restriction to the domain of offline testing since the method requires injection of a test signal into the transformer windings through the high-voltage bushings. To address the difficulties arising from this issue, in this contribution, a new technique for online transfer function monitoring of the power transformers windings through a quite simple, economic, and noninvasive capacitive sensor installed on the surface of the transformer bushing is presented. Interturn faults with various levels of severity were imposed on the winding of a 35-kV/400-V, 100-kVA oil-immersed distribution transformer to evaluate the feasibility and sensitivity of the method. The experimental results proved that the newly developed online monitoring system is feasible and sensitive to detect unambiguously interturn faults even down to 0.2% shorted turns along the winding. As such, the proposed approach in this paper enables timely warning of a rising failure and serves a better purpose in assessing the health of a faulty transformer.
39818
Kumar A. & Mahajan, S.M.
Time domain spectroscopy measurements for the insulation diagnosis of a current transformer
IEEE Trans. on Dielectrics and Electrical Insulation; Vol.18; No.5; October 2011; 1803 - 1811
There is a growing need for accurate but nonintrusive insulation diagnostic techniques and better maintenance tools to assay the internal condition of transformers. Classical diagnostic methods and periodic maintenance routines have been in practice for several decades. Some of the newer non-destructive diagnostic techniques are based on the measurement of dielectric response functions in time and frequency domain. Polarization and Depolarization Current (PDC) analysis is an on-site, off-line, time-domain diagnostic technique capable of differentiating the aging effects of paper and oil insulation. In this research work, a medium voltage (69 kV, 1200 A/5 A) current transformer (CT) was subjected to thermally accelerated tests. The elapsed insulation life was calculated as per IEEE C57.91-1995. Insulation diagnostic tests including PDC were performed at various aging stages of the CT. Results indicate that PDC tests can be applied to instrument transformers as well. A correlation between time and frequency domain spectroscopic measurements was also established. Measurement of furanic compounds in the oil was consistent with the paper conductivity trends observed in the PDC measurements.
14. OTHERS
39819
Motushi Kar et.al
A linear current injection generator for the generation of electrons in a nuclear reactor
Electrical India, Vol.51; No.11; November 2011; 256-259
While operating a nuclear reactor it is absolutely necessary for generating a chain reaction or fission. A chain reaction can be initiated by bombardment of a heavy nucleus with fast moving particles. One of the common methods used for generating a fast moving particle is injecting a very high voltage into a particle accelerator and accelerating high energy particle beams using machines like cyclotron, synchrotron, linear accelerators i.e. linac and similar equipment. These equipment are generated and run by several high voltage applications like simple high voltage DC systems and supplies or pulsed electron systems.
39820
Koyama Y. et.al
Modeling and Analysis for Simulation of Common-Mode Noises Produced by an Inverter-Driven Air Conditioner
IEEE Trans. on Industry Applications, Vol. 47; No.5; Sept.-Oct. 2011; 2166 – 2174
This paper presents an intensive discussion on conducted electromagnetic interference (EMI) emissions from an inverter-driven air conditioner. Common-mode voltages produced by the pulsewidth-modulated (PWM) inverter may cause a high-frequency leakage current. The use of a spectrum analyzer and a line-impedance stabilization network (LISN) makes it possible to refer the leakage current in the time domain to the conducted-EMI emission levels in the frequency domain, which are prescribed by the EMI regulations. Simulation-based estimation of the conducted-EMI emission levels in advance allows engineers to efficiently design a cost-effective EMI filter intended for meeting the regulations. This paper achieves modeling of the inverter-driven air conditioner with focus on common-mode voltages and leakage-current propagation paths. The simulation circuit developed can be used to predict conducted-EMI emission levels and to design the cost-effective EMI filter. Simulated results agree fairly with experimental ones in both cases of the EMI filter being connected and disconnected.
39821
Fujishima H.et.al
Development of Low-Emission Bio-Fuel Boiler System with Plasma-Chemical Hybrid
Reduction
IEEE Trans. on Industry Applications, Vol. 47; No.5; Sept.-Oct. 2011; 2210 - 2217
A pilot-scale low-emission boiler system consisting of a bio-fuel boiler and a plasma-chemical hybrid NOx removal system is investigated. This system can achieve carbon neutrality because the bio-fuel boiler uses waste vegetable oil (WVO) as one of the fuels. The plasma-chemical hybrid NOx removal system has two processes: NO oxidation by ozone produced from plasma ozonizers and NO2 removal using a Na2SO3 chemical scrubber. Test demonstrations of the system were carried out for mixed oils (mixture of heavy oil and WVO). A stable combustion was achieved for the mixed oil (20%-50% WVO). The properties of flue gas-e.g., O2, CO2, and NOx -when firing mixed oils were nearly the same as those when firing heavy oil for an average flue gas flow rate of 1000 Nm3/h. The NOx concentrations at the boiler outlet were 90-95 ppm. Furthermore, during a 300-min continuous operation when firing 20% mixed oil, a NOx removal efficiency of more than 90% was confirmed. This is equivalent to less than 10 ppm at the scrubber outlet when the flue gas flow rate was 870 Nm3/h. In addition, CO2 reduction when heavy oil was replaced with WVO was estimated. The system comparison is described between the plasma-chemical hybrid NOx removal and the conventional NOx removal.
39822
Yamamoto T. et.al
Novel
IEEE Trans. on Industry Applications, Vol. 47; No.5; Sept.-Oct. 2011; 2235 - 2240
Stringent NOx and volatile organic compound (VOC) flue gas regulation are set force for various industrial emission sources. The conventional emission control technologies such as selective catalytic reduction for NOx treatment and incineration and catalysts for VOC treatment have limitations in terms of operating conditions, costs, and performance. A novel, economical, and cost-effective device is mandated to meet the regulations. A new approach consists of flue gas adsorption, desorption (concentration and adsorbent regeneration), followed by nonthermal plasma decomposition. This concept was applied for NOx, various VOCs, and other hazardous air pollutant treatment. More than 90% of NOx and VOC reduction was achieved using a series of surface discharge units. The energy efficiencies of 3.35 g( NO2)/kWh for NOx and 34.2 g/kWh for toluene were achieved using concentration technique, followed by surface discharge plasma reactor. These hybrid processes make the flue gas volume order of magnitude small, resulting in the reduction of the energy yield, reactor size, power supply, and total system costs.
39823
Shimizu K. et.al
Removal of Indoor Air Contaminant by Atmospheric Microplasma
IEEE Trans. on Industry Applications, Vol. 47; No.6; Nov. – Dec. 2011; 2351 – 2358
Microplasma has advantages of reducing the power and downsizing the entire plasma system. Decomposition of formaldehyde (HCHO) by a microplasma reactor was demonstrated for improving indoor air quality. One experimental investigation used a one-pass treatment (5 L/min), and the second used a large-volume treatment (1500 L/min). The removal ratio of HCHO (initial concentration of 0.8 ppm) in the one-pass treatment was 96% at a discharge voltage of 1.3 kV using a high-voltage (HV) amplifier and a Marx generator with MOSFET switches as pulsed-power supplies. In the case of using the Marx generator, there was no generation. The removal ratio of HCHO (initial concentration of 0.5 ppm) in the large-volume treatment after 60 min was 51% at 1.2 kV when using the HV amplifier and considering 41% natural decay ratio of HCHO. The removal ratio was 54% at 1.2 kV with the Marx generator, and the natural decay ratio was 44% after 60 min of treatment.
39824
Kuwahara T. et.al
Improvement of Reduction Efficiency in Diesel Emission Control Using Nonthermal Plasma Combined Exhaust Gas Recirculation Process
IEEE Trans. on Industry Applications, Vol. 47; No.6; Nov. – Dec. 2011; 2359 - 2366
Atmospheric-pressure nonequilibrium nonthermal plasma hybrid exhaust gas aftertreatment systems that do not utilize precious metal catalysts, harmful ammonia, etc., have been developed by the authors. Two types of new environmental protection systems (a dry system and a wet system), which enable the production of ultralow , particulate matter and emissions as well as reduced fuel consumption and low cost, are investigated for diesel engines, marine engines, and combustion boiler applications. This paper reports the principles of the dry system and some recent experimental results of laboratory tests. The reduction comprises three flow processes: 1) adsorption, 2) heating, and 3) cooling processes. The heating process corresponds to the regeneration process. These processes are repeated in the following order: 1), 2), and 3). This dry system demonstrates excellent energy efficiencies that meet the most recent Japanese national regulations regarding automobile diesel engine exhaust gas. In this study, approximately 60% of the of the exhaust (: 240 325 ppm, , N: standard state) can be treated for 35 h. An improved system energy efficiency of 143 , which is the highest yet, is achieved for reduction.
39825
Adamiak K. & Floryan, J. M.
Dynamics of Water Droplet Distortion and Breakup in a Uniform Electric Field
IEEE Trans. on Industry Applications, Vol. 47; No.6; Nov. – Dec. 2011; 2374 – 2383
Distortion of a free droplet in a uniform electric field is studied numerically using the boundary element method. It is assumed that the droplet is made of an ideally conducting liquid. There exists a critical magnitude of the electric field intensity. The droplet oscillates for weaker electric fields and elongates until a thin jet emanating from the droplet tip is formed for stronger electric fields. Numerical predictions agree reasonably well with the available experimental data.
39826
Podlinski J. et.al
Electrohydrodynamic secondary flow and particle collection efficiency in a one-sided spike-plate type electrostatic precipitator
IEEE Trans. on Dielectrics & Electrical Insulation, Vol. 18; No.5; October 2011; 1401 - 1407
In this work, results of electrohydrodynamic secondary flow and particle collection efficiency measurements in an electrostatic precipitator under positive and negative voltage polarity are presented. The electrostatic precipitator had two plate collecting electrodes and a single spike discharge electrode. The spike tips were only on one side of the discharge electrode, therefore called a one-sided spike electrode. The electrohydrodynamic secondary flow pattern and collection efficiency measurements were carried out for two one-sided spike electrode positions: with the spike tips directed either upstream or downstream the primary flow. The results of the flow pattern measurement showed different flow patterns for different spike tips positions in respect to the primary flow direction. The electrostatic precipitator collection efficiency measurements clearly showed difference in the particle collection for both spike tips positions. Since the other electrostatic precipitator working parameters were the same, it can be concluded that the observed change of the electrohydrodynamic secondary flow was the main reason of the difference in the electrostatic precipitator collection efficiency.
39827
Niewulis, A et.al
Collection efficiency in narrow electrostatic precipitators with a longitudinal or transverse wire electrode
IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 18; No.5; October 2011; 1423-1428
Recently narrow electrostatic precipitators (ESPs) have become a subject of interest because of their possible application in diesel engine exhaust systems. In this work, results of particle collection efficiency measurements in narrow electrostatic precipitators for negative and positive dc voltage polarity are presented. The ESP used in this work was a parallelepiped equipped with wire discharge electrode and two collecting plate-electrodes. The experiments were carried out for two discharge electrode positions: longitudinally or transversely to the main flow direction. The obtained results showed that the collection efficiency strongly depends on the discharge electrode position. It is higher in the ESP with longitudinally-to-flow placed discharge electrode. The collection efficiency is also influenced by the EHD secondary flow generated in the ESP. The EHD secondary flow with high migration velocity (y-component of the particle velocity) and low turbulence intensity increase the chance of the particle deposition on the collecting electrodes.
39828
Farnoosh N.et.al
Numerical calculations of submicron particle removal in a spike-plate electrostatic precipitator
IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 18; No.5; October 2011; 1439 - 1452
A 3D hybrid Finite Element (FE)-Flux Corrected Transport (FCT) numerical algorithm is proposed to evaluate the electrical characteristics of a laboratory scale single stage spikeplate electrostatic precipitator and to predict the collection of submicron particles with diameters in the range of 0.25-1.5 μm. The precipitator consists of two parallel collecting plates with a spiked electrode mounted at the center, parallel to the planes and excited with a high negative dc voltage. The complex interaction between the electric field, fluid dynamics and the particulate flow in this precipitator are taken into account in the simulation. Particles are assumed to be charged by combined field and diffusion charging mechanisms. Motion of submicron particles under electrostatic and aerodynamic forces in turbulent flow is calculated using a Lagrangian-type Discrete Random Walk (DRW) model and User Defined Functions (UDFs) feature of the commercial FLUENT 6.2 software. The electrohydrodynamic secondary flow patterns, particle migration velocity patterns and particle collection efficiencies are examined for three different corona discharge electrode configurations: spikes located only on one side of the electrode with the tips directed either upstream or downstream of the channel, and spikes located on both sides. For a given particle concentration at inlet, the particle deposition rate along the channel and the average charge-to-mass ratios are evaluated for different particle sizes and applied voltages. Finally, the influence of particle concentration on particle collection efficiency for the ESP with spikes on two sides is investigated for -30 kV applied voltage. In selected cases, the numerical results are compared with the existing experimental data.
39829
Bilici M. et.al
Tribocharging and electrostatic separation of mixed granular solids in fluidized bed devices
IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 18; No.5; October 2011; 1476 - 1483
Granular materials, when fluidized by air or other gaseous medium, acquire electrostatic charge by inter-particle and particle-wall collisions. The effectiveness of particle tribocharging achieved with such fluidization process is crucial for establishing the feasibility of electrostatic separation of mixed granular solid wastes in the recycling industry. The present paper aims at a crude evaluation of the effects of the main factors that influence the efficiency of such a tribocharger, in the presence of an electric field orthogonally oriented to the direction of the fluidization air. The experiments were carried out on binary mixtures taking combinations of two of the three polymeric materials in different tests: (a) virgin polyamide, (b) polycarbonate and (c) polyacetal granules. The variables investigated were the duration of the tribocharging process, the level of the high-voltage applied to the electrode and the composition of the mixture. The analysis of the experimental data revealed the effects of each variable on the mass and the charge of the granules collected at the electrodes.