Burnt Breaker

[kingbambina]

Hi,

I need some help with investigating a burnt circuit breaker that feeds a compressor's motor. As you can see in the drawing attached, the voltage is 400V and a molded case circuit breaker that feeds the motor was burned at one phase only as an alarm was flagged of the motor overloading. As per the control circuit, I see that the breaker failed to open due to the overload but I cannot think of any reason why other than the phase that was damaged didn't age that well?

Any insight guys that can guide me on how to start this investigation?

Thanks

 

[kingbambina]

Diagram

 

[3DDave]

 

[cranky108]

Maybe that phase did not close with enough spring behind it to keep it completely closed.

 

[TugboatEng]

The breaker appears to be tripped. Was the interrupt eating sufficient for the source?

 

[kingbambina]

Yeah we had no past issues with these MCCBs. It might be a malfunction on that specific phase.

 

[TugboatEng]

A malfunction on a specific phase is normally what cause a breaker to trip and clear. Your trip didn't clear. What is the interrupt rating or the breaker. What is the power source? Transformer? Generator? Is there a DC component to the source power?

 

[wcaseyharman]

I was not able to see the diagram, but I am assuming this is a combination starter and there is a separate motor contactor and the thermal overload was tripped which dropped out the contactor. If that’s the case I wonder if we are looking at a breaker where one pole didn’t fully close and it overheated and burned open, single phasing the motor and causing the motor overload to operate.

We’ve had somewhat similar issues in the past, though not specially on MCCBs.

 

[kingbambina]

The interrupt rating is 400A. It's an MCC fed from a transformer and there is DC for the emergency stop switch.

 

[RRaghunath]

Any abnormality observed on compressor side, such as shaft jammed or with blades or with bearings??
Is there also a separate motor protection relay and a power contactor for this feeder??

R Raghunath

 

[TugboatEng]

Interrupt rating should be many thousands of amps. The required interrupt rating depends on the source of power (transformer or generator size).