Circuit Breakers is Protective Device used in Power System to make or Break the Circuit. 

Definition:

CB is an Onload Switching Device, which can operate Manually for Controlling in Normal Conditions and Operate Automatically for Protection during Faults.

Construction:

  1. Main/Power ContactsUsed 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. Operating Shaft: Movable Contact is connected to the Operating Shaft. When the Operating Shaft moves down , the Breaker opens and when it goes up , the Breaker closes.
  3. 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 indication and Protecting the Trip Coil and Closing Coil.                                      
  4. Operating Mechanism:
  5. Control Circuit:

To know the difference between Main/Power Contacts and Auxillary contacts of the Breaker

Working:

  1. When the Breaker is ON/Closed, the two contacts (Fixed contact and Moving Contact) are physically connected to each other by the applied Mechanical pressure on the Moving Contact.