Online Fault Sensor for Transformer

Electrical Research and Development Association (ERDA)

Today, Power transformer is one of the primary components of power distribution network. Hence protection of transformer is most important. A number of means for transformer protection against incipient fault are available. Buchholz relay and DGA methods are used invariably. However, these conventional methods have some limitations.

Limitations of Buchholz Relay: Whenever transformer is overloaded for long time period, gases are released which get dissolved in transformer oil. Buchholz relay is being used in transformers as a safety device, since the evolution of transformer. It protects the transformer from the faults occurring inside the transformer such as impulse breakdown of the insulating oil, insulation failure of turns, etc. But Buchholz relay is found to be slow and detects fault at a later stage and is not sensitive to low intensity faults. Moreover, in case of minor earthquake, this device gives a false alarm and trips the transformer. Further, this relay does not have provision of data monitoring and data logging.

Limitation of DGA: Condition monitoring through Dissolved Gas Analysis (DGA) is found reliable and well proven tool to detect any abnormality / fault inside the oil filled transformer at initial stages of development. This helps the utility to take remedial action well in time, to avoid any premature failure. DGA, although a reliable technique, is an offline method. Moreover, improper sampling may lead to erroneous results. 

In view of above mentioned limitations of the existing methods of incipient fault detection in transformers, Electrical Research & Development Association (ERDA) has designed and developed Hydrogen based online fault detection system for early detection of faults in transformer.

Working Principle of Online Fault Detection System

In case of fault – electrical or thermal, hydrogen gas evolves as a result of degradation of transformer oil. When the evolved hydrogen gas, reaches the sensor head, sensing element will detect it and produce an equivalent electrical signal, which is transmitted through a screened cable to control unit. Control unit houses display unit which shows relative concentration of hydrogen in transformer tank. User can set preset values to trigger alarm / action depending upon severity of fault.

System Description

This system mainly consists of two parts: sensor head and display cum control unit. The sensor head mainly consist of hydrogen sensor. The electrical resistance of the sensor varies with change in quantity of hydrogen gas in the air. After compensation for change in temperature and humidity, the signal is fed to controller for processing. In display cum control unit, microcontroller is used for signal processing of the data obtained from sensor head. This unit generates equivalent hydrogen in ppm for display and annunciation.

Product Information

  • Sensor for transformer – senses hydrogen gas emitted as a result of fault inside the transformer.
  • To be installed in addition to Buchholz relay
  • It has two components
    • Sensor Head – directly mounted on the air vent port of the Buchholz relay
    • Display cum Control Unit – mounted in the marshalling box near the transformer
  • Different threshold values setting for tripping during fault.

Distinctive Features

  • Detection of  minutest hydrogen gas liberated as low as 50 ppm
  • Incipient fault detection at an early stage
  • Data logging
  • Remote monitoring
  • Different threshold values setting for tripping during fault


  • Gas response: Hydrogen
  • Measurement range: 0-1000 ppm of hydrogen equivalent
  • Accuracy: ± 10% of reading
  • Sensor principle: Gas permeable membrane and solid state hydrogen gas detector
  • Communication: RS 232


  • Operates at lower gas pressure compared to Buchholz relay
  • Incipient fault detection at an early stage
  • Facility of Data logging and remote monitoring
  • Different threshold values setting for tripping during fault
  • Economical
  • Easy to install
  • Retrofit

Patents Granted

  • Title – An online fault sensor for oil filled transformer. Patent Number: 204691
  • An improved online incipient fault sensor device for detection of incipient fault in oil-filled electrical apparatuses such as a transformer. Patent Number: 341056

Pictorial Representation of Technology

Figure 1 : Pictorial presentation of On-line Fault Sensor

Figure 2 : Online fault sensor with control unit


Leadership Team

Dr. Satish Chetwani


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Dr. Uday Puntambekar

Asst. Director & Head of Division Mechanical and Insulating Materials, Rajahmundry, Purchase

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Mr. Rajib Chattopadhyay

Sr. Manager & Head of Division PETE II (Impulse, Cable, CT-PT, Calibration), Rabale, Narol, ERDA North, Maintenance, (Electrical & Civil)

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Mr. Yashinkhan Pathan

Sr. Manager & Head of Division PETE I (Transformers, Switchgear, Short Circuit – Makarpura & Savli)

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