1.Main contacts (Power contacts):
  • The main contacts of a breaker are used to Interrupt the flow of the current & Hence the power rating of these contacts will be high.
  • The Main Contacts have a Fixed part & a Moving Part and there is an Arc Extingushing Medium between the two parts which extinguishes the arc, during opening of the Poles.
2.Auxillary contacts:
  • Before understanding the Auxillary contacts, we have see what is an Auxillary Switch.
  • Auxillary  Switch is a Switch which is Mechanically attached to the Main Contact (Moving Contact)  of the CB and Operates when the Breaker changes its Position (From On to OFF or from OFF to ON).
  • Now, the when the Auxillary Switch operates, its Contacts (Called as Auxillary Contacts)  changes its status i.e from Open to Close & Close to Open  and hence can be used in the Breaker Control circuit  for Following Purpose:
    • Breaker Trip Ckt & Bkr Closing Ckt for the Protection of Trip Coil & Closing Coil.
    • For the Breaker ON/OFF Indication.
    • TCS Relay.
    • Busbar Relay
    • SCADA
  • Please Note that Auxillary Contacts are Electrically Isolated from the Mian Contacts & are used to represent the Main Contacts.
  •  Use of Auxillary Contacts in Trip Circuit & Closing Circuit: When the breaker is open, contact 52a (NO) in the Trip Circuit is open  and contact 52b (NC) in the Close Circuit  will be Close. When the Breaker changes its Position from OFF to ON, contact 52a (NO) in the Trip Circuit becomes Close  and contact 52b (NC) in the Close Circuit  will becomes Open. Now, if there is a Continous Juice coming from somewhere, the Tripping Coil or the Closing will not get burnt, as the Auxillary will have already opened the Trip or the Close Circuit, therby protecting the Trip or the Close Coil.
  • For Breaker ON/OFF Indication: We give Indication Positive (L1)  to one end of a NO & NC Auxillary contact, the other end of the NC Contact is connected to Breaker OFF LED & the other end of NO Contact is connected to the Breaker ON Led. A Continous Indication Negative (L2) is given to the other end of the LED’s.
  • For TCS Relays: For complete working of the TCS Relays please check the link : https://electricalfundaz.com/trip-circuit-supervision-relay-explained/
  • Busbar Relay: Breaker Auxillary Contacts are used to give Breaker Status (ON/OFF) to the Busbar Relay.
  • SCADA: For the Breaker ON/OFF Indication.

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