Circuit Breaker trip caused by utility fault?

[genhead]

A commercial building is supplied through a 630amp 415v circuit breaker. On two occasions this circuit breaker has tripped (overcurrent or short circuit) after utility faults have occurred nearby. One of the faults was caused by a vehicle hitting a power pole, I'm not sure about the other one.
The circuit breaker does not have any shunt trip or under-voltage releases fitted.
What would cause this circuit breaker to trip?

 

[jghrist]

Was the fault cause an outage to the building? If so, did the breaker trip when the power went out or when it came back on? If the outage was momentary, you may not be able to tell. If the fault was on a different circuit and there was no outage, there may have been a voltage dip that caused an increase in current in motors.

 

[itsmoked]

If you have cars hitting power poles then there could be several reasons for your breaker tripping.

1) A lost phase. This can cause the current to spike in other phases. Your breaker could notice a ground fault problem.

2) Large spikes from motors losing power very briefly.

3) Low voltage causing motors to draw excessive current.

4) ?? What else guys?

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[windie]

4) The motors on your system may be supplying fault current to the fault on the utility system. During the first few cycles of the fault this could be close to the DOL starting current of the motors.

 

[powerjunx]

windie, itsmoked and jghrist have good assessment to your query.
"4) The motors on your system may be supplying fault current to the fault on the utility system. During the first few cycles of the fault this could be close to the DOL starting current of the motors."..you're on the right track! COnsidering, you have a large machines this will contribute about 30% reactance to the fault.

If you need to be isolated during FAULTS, why not used directional overcurrent relay?