Relays and circuit breaker combination

Operation Mechanism of a Circuit Breaker

Energy Storage and Release

A closed circuit breaker (CB) stores sufficient energy in one form or another to open its contacts. When a protective relay signals to open the circuit, this stored energy is released, causing the circuit breaker to trip and open.

Connection Between Relay and Circuit Breaker

Except in special cases where protective relays are mounted directly on the breaker, the connection between the relay and the circuit breaker is typically achieved through hard wiring. The figure schematically indicates this association between the relay and the circuit breaker.

Key Components in Protection

In protection systems, the critical components of the circuit breaker include:

• Trip Coil: Initiates the tripping action of the circuit breaker.
• Latching Mechanism: Holds the circuit breaker in the closed position and allows for rapid release when necessary.
• Main Contacts: The components responsible for physically interrupting the circuit current.
• Auxiliary Contacts: Used in various ways within control and protection circuits.

Fault Isolation Process

The roles played by these components during the fault isolation process are as follows:

• Information Reception and Analysis: The relay receives information, analyzes it, and determines that the circuit should be opened.
• Activation of Trip Coil: The relay closes its contacts, energizing the trip coil of the circuit breaker.
• Unlatching and Opening Main Contacts: The circuit breaker unlatches and opens its main contacts under the control of the tripping spring.
• De-energization of Trip Coil: The trip coil is de-energized by the opening of the circuit breaker’s auxiliary contacts.

Applications of Auxiliary Contacts

Circuit breakers are typically equipped with multiple auxiliary contacts, which serve various purposes in control and protection circuits, such as indicating the position of the circuit breaker or providing interlocking functions.