High Voltage Circuit BreakerHV AC Switchgear

Auxiliary contact in switchgears

Auxiliary contacts are contacts that show the circuit breaker or switchgear position.
At least one contact is used in each control circuit (trip / close) to control the coil supply.
Contacts not used in control circuits, are normally connected to terminals for customer use.
Normal total quantities: 12 NO+12 NC , 18 NO+18 NC, 20 NO+20 NC .
When the Auxiliary Switch operates, its Contacts changes its status from Open to Close & Close to Open and hence can be used in the Breaker for Following Purpose:

  • Breaker Trip & Closing for the Protection of Trip Coil & Closing Coil.
  • For the Breaker ON/OFF Indication.
  • TCS Relay.
  • Busbar Relay
  • SCADA

NC-contact (normally closed contact) is a closed contact when device is not energized or in the drawn situation, according to circuit diagram.
NO-contact (normally open contact) is an open contact in the same situation.
NOC-contact (normally open-closed contact) is a closed contact that opens and an open contact that closes with a common backside when changing position. Could also be called: Change-over contact.
In figure Left can see auxiliary switch and in right can see AUX switch circuit diagram in circuit breaker operating mechanism.

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