MV AC Switchgear

Switchgears earthing in prefabricated substation acc to IEC

A main earthing conductor system shall be provided to connect to the earth all metallic parts of the prefabricated substation not belonging to the main and secondary/auxiliary circuits of the equipment.
The main earthing conductor system shall be capable of carrying the rated short time and peak phase to earth withstand currents from each element of the prefabricated substation to the external earthing connection, under the neutral earthing condition of the system.
Earth system shall be taking into account the thermal and mechanical stresses caused by the current it may have to carry.

Components to be connected to the earthing circuit shall include:

  • the enclosure of the prefabricated substation if it is metallic;
  • the enclosure, if metallic, of the high voltage switchgear from the terminal provided for that purpose
  • the metal shields and the earthing conductors of the high-voltage cables
  • the transformer tank or metal frame of dry-type transformers
  • the frame and/or enclosure, if metallic, of the low voltage switchgear
  • the earthing connection of automatic controls and remote-control devices

In this figure show an example of earthing system in prefabricated substation.

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