Transformer protection

Power transformers are critical in the power grid. They have a long lead time for repair and replacement. Consequently, transformer protection has to limit the damage to a faulted transformer. Some protection functions, such as over-excitation protection and temperature-based protection can identify operating conditions that may cause transformer failure.

Failures in transformers can be classified into:

  • Winding failures due to short circuits (turn-turn faults, phase-phase faults, phase-ground, open winding)
  • Core faults (core insulation failure, shorted lamination)
  • Terminal failures (open leads, loose connections, short circuits)
  • On-load tap changer failures (mechanical, electrical, short circuit, overheating)

ABB's transformer protection relays are used for protection, control, measurement and supervision of power transformers, unit and step-up transformers, including power generator-transformer blocks in utility and industry power distribution networks. The relays provide main protection for two-winding power transformers and power generator-transformer blocks.


  • Flexible transformer protection relay for two-winding power transformers

Product benefits

  • Limits the damage to a faulted transformer
  • May identify operating conditions that may cause transformer failure

Product features

  • Differential protection, thermal overload protection, voltage protection and automatic voltage regulator
  • Configurable functionality to meet specific requirements of different applications

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