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ERDA NEWS, VOLUME: 41, ISSUE: 4 (October to December 2024)
Root Cause Analysis (RCA) of Failed Components and R&D Projects
A. Root Cause Analysis (RCA)
i) Root Cause analysis of Failed Aluminium Flange of Transformer Bushing
Root cause analysis of failed aluminium flange of transformer bushing was carried out for a high voltage bushings manufacturer. Aluminium flange was found damaged before the installation at site. Investigation of failed flange was done using fractography analysis, microscopic examination (optical, SEM and EDS), material composition and mechanical testing and FEM stress analysis of components considering different loading conditions. Visual examination and fractography analysis showed that crack formed on outer side of flange near center interface region.
The cracks in the material resulted from:
- Material composition did not meet the specified composition
- Fractography and microstructural analysis indicated the presence of casting defects (porosity) at the failure region and presence of micro cracks formed at unwanted detrimental Fe rich needle shape precipitates (AlFeSiMn) in the microstructure (Figure i). The defect in materials observed to cause inferior mechanical properties of flange material and assisted in cracking of flange.
- The FEM analysis of flange carried out to investigate the stress condition of cracking, indicated that bending load above 1 MPa (10 bar) on flange can generate the stress concentration region near the interface to initiate the cracks as observed on flange (Figure i).
Therefore, it was inferred from the detailed analysis that the presence of defects in material (porosity and detrimental Fe rich precipitate) under bending overload condition might have led to failure of flange before the installation. As the failure of aluminium flange before installation had possibly occurred due to inferior flange material under bending overload condition. Suitable recommendations were given related to manufacturing process so that mechanical properties as per design specifications are achieved.
ii) Root Cause analysis of Failed 400 kV Composite Insulators
Root cause analysis (RCA) was conducted on failed 400 kV composite insulator as shown in photograph in Figure (ii). The insulator failed after service life of 13 years. Due to its premature failure the utility approached ERDA for Root Cause Analysis (RCA) of the failed insulators and assessing condition of working insulators. For the RCA, two failed and one working insulator were evaluated. The insulators were located in the salt creek area with high humidity and temperature.
Two as received failed insulators were broken at line end and it showed degradation of composite rod. Silicone rubber from the insulators was brittle and found to have undergone chemical degradation. Microscopic observations showed cracks in the silicone rubber which led to entry of water/moisture at the silicone-composite rod interface. The water diffusion led to degradation of composite rod at the line end due to presence of enhanced electric field. Properties of the composite rod also showed degradation. The interfacial strength between the composite rod and silicone rubber was found good. Local environmental conditions were critical factor that led to degradation and failure of the insulators. It was recommended to replace the faulty insulators on a section of the transmission line.
B. R&D Projects
R&D division of ERDA completed Contract Research Project titled “Thermal Performance analysis of different radiator designs with respect to various transformer oil types”. This project was sponsored by a leading private company. Transformer radiator plays a crucial role in dissipating the generated heat. Typically, radiators are positioned on the sides of the transformer and use circulating oil to transfer heat away. The size and number of radiators are determined based on the transformer’s design calculations, ensuring adequate cooling capacity.
Traditionally, mineral oil has been the preferred dielectric fluid for transformers. However, recent trends favour ester based oils due to their superior environmental performance. This change in oil type can impact the cooling efficiency of a given radiator design. Therefore, it is essential to assess the radiator’s performance with different types of insulating oils to optimize transformer design and ensure efficient thermal management. Experimental setup was prepared at ERDA to carry out various experiments. Experimental results were analysed with the help of various simulation tools / equations and solutions were proposed as an outcome of the project.
C. Testing / Simulation Study Conducted for Customer
i) Electrical Field Analysis of 33kV Vacuum Circuit Breaker by FEM approach
A 33 kV Vacuum circuit Breaker Analysis was undertaken for the client by using the Finite Element Method Approach. Specifically, the work involved detailed electrostatic field mapping (Electric Field) at System Voltage, peak Impulse Voltage and Power Frequency Voltage level on Bushing Insulator, Pole Housing and Spout of VCB. The electric field Strength at various locations were mapped as per following figures.
ii) Testing of 300 kVA transformer
R&D team of ERDA carried out special tests on 300 kVA amorphous core transformer for a customer. The purpose of the testing was to study the behavior of various losses in transformer for various input supply like pure sinusoidal ac voltage at 60 Hz, ac voltage having DC bias, ac voltage having desired harmonics etc. Grid simulator was used to create required input ac voltage condition for the transformer.
iii) Condition Assessment and Performance Monitoring of Solar PV Module through Thermal Imaging and I-V Characteristics
Due to continuous increase in energy demand & exhaust of fossil fuel, demand of solar power plant and its installation is increasing significantly as clean, abundant & green source of energy. The ROI calculation for solar systems often assumes 20-25 years of power production which is based on the concept of gradual power loss due to aging of panels. These calculations don’t consider system deterioration caused by lightning storms, panel cell overheating and other failures developed during service or operation of module. However, significant power loss occurs due to these failures or sometimes due to high temperature of hot spot in extreme conditions may lead to fire and possibility of heavy damage of solar power plant.
ERDA developed new test facility to find various types of damages that take place in solar PV Module during its service condition through Thermography, Ultraviolet Fluorescence, Electroluminescence techniques & performance output to know the power output of solar panel through I-V tracer.
Failure Identification & Performance Monitoring Methods
A. Visual Inspection
Visual examination is a powerful tool and the best method to find defects in solar module. It is rapid and applicable to all types of PV module.
B. Thermography Inspection
Thermography technique is used to find defect which are not visible during visual examination in the field. Thermography identifies the increased temperature (hot spots) at localized area as compared to the surrounding area. It helps in fast identification of loose, corroded connections even if they are not visible to naked eye. It can be a driver in making predictive and preventive maintenance schedules.
C. Ultraviolet Fluorescence testing – UVF of PV Module
UVF (Ultraviolet Fluorescence) testing is used to find defects and degradation. UVF testing uses ultraviolet light to excite fluorescent dyes or defects in the module, which then emit visible light. This visible light is captured by a camera or sensor, revealing defects or degradation.
D. Electroluminescence testing – EL of PV Module
EL (Electroluminescence) testing is used to find defects and degradation. EL testing involves applying a forward bias voltage to the module, causing the silicon cells to emit light. This light is then captured by a camera or sensor, revealing defects or degradation.
E. I-V Curve of PV Module
Power Loss (Pmax) in the PV module can be identified by I-V curve. A Portable I-V tracer is used for measurement of I-V Curve under Natural Sunlight Condition which should be corrected with Standard Test Conditions (1000 W/m2, 25°C). Pyrometer or Sunlight Irradiance Sensor is used as a reference for Solar Device for Irradiance. Fill Factor (Solar Cell) determines the maximum Power from a solar cell. Typical Fill Factor ranges from 50% to 82%.
Case Studies
A) Corrosion at Bus bar Side (Green Effect) Polycrystalline Module
B) Defective Bypass in Polycrystalline PV Modules
Conclusion
- Degradation or failure may happen in PV modules in many ways during the Operations, which can depend on many factors like design, manufacturing process, quality of materials, transportation etc.
- Thermography, Ultraviolet Fluorescence, Electroluminescence & I-V Curve techniques are useful to identify the faults in advance and resulting power loss due to various faults associated with Solar PV module.
- Thus we can control the power generation losses, increase reliability and availability of power and asset management of Solar PV power plant.