Trip Circuit Supervision design

[Meh]

Hi,

I am working on TCS on MV switchboard. I have a question about using external resistor in "CB Open" circuit and not having the external resistor in "CB Close" condition. In both statuses, the current is going through the trip coil. How come when we are supervising the trip circuit with "CB Close" status we don't need to limit the current but when we are supervising the trip circuit with "CB Open" status, we need to add the external resistor?

Thanks

[Manon_Chaboud · Accepted solution]

hello @Meh !

In the context of supervising the trip circuit with "CB Open" and "CB Close" statuses, the use of an external resistor serves different purposes based on the specific conditions. Here's a breakdown:

1. CB Open Status:

   • When supervising the trip circuit with the circuit breaker in the "CB Open" status, adding an external resistor is necessary to limit the current. This is because the trip coil is in the circuit, and the external resistor helps limit the current flow to a safe level, preventing excessive current from damaging the trip coil or associated components.

2. CB Close Status:

   • In the "CB Close" status, the trip coil is still in the circuit, but the need for an external resistor is not present. This is likely because the circuit design or the specific characteristics of the "CB Close" status do not require current limitation for the proper functioning of the trip circuit.

The decision to include an external resistor in the "CB Open" status and not in the "CB Close" status likely reflects the specific operational and safety requirements for each condition. It's important to follow the manufacturer's guidelines and relevant standards when implementing such supervisory circuits to ensure proper functioning and safety.