Auxiliary contact in switchgears

Auxiliary contacts are essential components in circuit breakers and switchgear, providing critical functionality for control and indication. Here's a breakdown of their purpose and operation:

Purpose of Auxiliary Contacts:

1. Breaker Trip & Closing Control:

• Auxiliary contacts are used in control circuits to manage the supply to the trip coil and closing coil, ensuring proper operation of the circuit breaker.

2. Breaker ON/OFF Indication:

• These contacts provide signals to indicate whether the breaker is in the ON (closed) or OFF (open) position.

3. Integration with Relays and SCADA:

• Auxiliary contacts are connected to devices like the Trip Circuit Supervision (TCS) relay, busbar relay, and SCADA systems for monitoring and control purposes.

4. Customer Use:

• Contacts not used in control circuits are typically made available to customers for custom applications.

Types of Contacts:

1. NO (Normally Open) Contact:

• Open when the device is not energized or in its default state.

• Closes when the device is energized or activated.

2. NC (Normally Closed) Contact:

• Closed when the device is not energized or in its default state.

• Opens when the device is energized or activated.

3. NOC (Normally Open-Closed) Contact (Change-Over Contact):

• A combination of NO and NC contacts with a common backside.

• When the device changes position, the NO contact closes, and the NC contact opens simultaneously.

Operation of Auxiliary Switch:

• When the auxiliary switch operates, its contacts change their status:

• Open contacts become closed.

• Closed contacts become open.

• This change in status is used for various control and indication functions in the circuit breaker.

Typical Quantities of Auxiliary Contacts:

• Auxiliary switches are often provided in standard configurations, such as:

• 12 NO + 12 NC

• 18 NO + 18 NC

• 20 NO + 20 NC

Circuit Diagram Representation:

• In the circuit diagram, the auxiliary switch is typically shown with its NO, NC, and NOC contacts, illustrating how they interact with the breaker's operating mechanism.