×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Circuit Breaker trip caused by utility fault?

Circuit Breaker trip caused by utility fault?

Circuit Breaker trip caused by utility fault?

(OP)
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?

RE: Circuit Breaker trip caused by utility fault?

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.

RE: Circuit Breaker trip caused by utility fault?

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

RE: Circuit Breaker trip caused by utility fault?

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.

RE: Circuit Breaker trip caused by utility fault?

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?

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources