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Transformer protection

Hitachi Energy's protection solutions are designed to ensure safe and reliable operation of the transformer and auto-transformer feeders for distribution, sub-transmission, and transmission systems. 

Protection solutions for transformers are designed to accommodate different busbar arrangements across all voltage levels and for high-voltage autotransformers. The solutions are intended for the following types of configuration:

  1. Two- and three-winding transformers in different configurations
  2. Autotransformers, with or without loaded tertiary winding

The protection functions are split between two groups of hardware (group 1 and group 2) to ensure good reliability. Different protection functions can be allocated to either of the groups, but typical arrangements are as follows:

Group 1 protection unit, basic version


  • Biased differential protection for transformers / autotransformers
  • Current- and thermal-overload protection
  • Voltage protection
  • Overexcitation
  • Disturbance recorder
Group 2 protection unit, basic version
  • High-impedance/low-impedance restricted earth-fault (REF) protection on the primary and/or secondary winding for transformers
  • Per-phase high-impedance protection (for autotransformers)
  • Non-directional overcurrent protection
  • Tertiary earth-fault protection
  • Disturbance recorder
  • Busbar and breaker-failure protection schemes (decentralized) can be accommodated in transformer protection solutions.

Get to know more

  • Biased differential protection for transformers /autotransformers
  • Phase-segregated high-impedance protection
  • High-impedance/low-impedance restricted earth fault (REF) protections on the primary and/or secondary side
  • Tertiary earth fault protection
  • Transformer differential protection can be an integrated part of the station protection bay unit
  • Non-directional E/F overcurrent protection
  • Phase overcurrent protection
  • Thermal overload 
  • Over fluxing protection 
  • Overvoltage protection 
  • Logic for Buchholz, winding, oil temperature etc.
  • Transformer guard units for eight mechanical protection signals like Buchholz
  • Disturbance recorder
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