What is the use of an earthing transformer?


An earthing transformer is a type of auxiliary transformer that is used to provide a ground path for an ungrounded or delta-connected system. ¹ It is also called a grounding transformer or a neutral coupler. ² The main uses of an earthing transformer are:

  • To maintain the system neutral at or near ground potential and limit the transient overvoltages during faults. ¹
  • To provide a source of ground fault current that can be detected and cleared by protective relays. ¹
  • To allow the connection of phase-to-neutral loads that require a neutral point. ¹²

An earthing transformer can have different winding configurations, such as zigzag, star, or delta-wye.

¹² The most common one is the zigzag configuration, which has a high magnetizing impedance for normal currents but a low impedance for zero-sequence currents during faults. ² This way, the earthing transformer can provide a stable voltage and current for the system and the loads. ²

The rated voltage of an earthing transformer is the line-to-line voltage of the system, and the current rating is the maximum neutral current that it can carry during faults.

Earthing transformers are usually installed at the substation or near the generator of the power system. ³ They are part of the earthing system of the network and help to improve the safety and reliability of the power supply.