Typical mechanical interlocks role for draw out circuit breakers in LV switchgears according to IEEE standard

Safety Features and Requirements for Circuit Breakers

• Interlocking to Prevent Unauthorized Movement: To ensure operational safety, it is imperative to prevent the movement of a circuit breaker to or from the connected position when the circuit breaker itself is in the closed state. This safeguard helps avoid potential electrical hazards and damage to the equipment.

• Pre - closing Conditions: Additionally, measures are in place to prevent the closing of the circuit breaker unless the primary disconnecting devices are either in full electrical contact or separated by a distance sufficient to ensure safety. This requirement guarantees that the electrical system is properly configured before the circuit breaker is closed.

• Stored Energy Mechanism Protection: Circuit breakers equipped with stored energy mechanisms must be designed with specific safety features. These mechanisms should be engineered to prevent the release of stored energy unless the mechanism has been fully charged. To protect operators and service personnel from the risks associated with accidental energy discharge, the following protective measures can be implemented:

1. Housing - based Interlocks: Interlocks within the circuit breaker housing can be utilized. These interlocks prevent the complete withdrawal of the circuit breaker from the housing when the stored energy mechanism is charged, thereby ensuring that the energy remains safely contained during normal operations.

2. Closing Function Blocking Devices: A suitable device can be installed to prevent the circuit breaker from being fully withdrawn until the closing function is blocked. This ensures that any potential energy release during the withdrawal process is avoided.

3. Automatic Discharge Mechanisms: An automatic energy - discharge mechanism can be incorporated. This mechanism will discharge the stored energy during the process of withdrawing the circuit breaker from the housing, eliminating the risk of accidental energy release and providing enhanced safety for maintenance and operation.

The accompanying picture illustrates a draw - out circuit breaker from EATON, which is typically used in low - voltage (LV) switchgear, and showcases how these safety features may be integrated into practical electrical equipment.