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.