Random tripping problem

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alan mcneil

Member
Location
Massachusetts
At our facility we have Westinghouse circuit breakers that were installed about 30 years ago.

These breakers have an electronic sensor for instantaneous trip settings, most of the frames are for 600 amp and have a plug in "button" for 600 through 150 amps settings.

Lately we have had some of these breakers trip for no APPARENT reason, today a 200 amp breaker tripped.

The load on this breaker is only around 70 amps and all the connections are tight, this particular circuit breaker has been tested and calibrated just last month.

We have had this problem with other circuit breakers in this same MDP.
Code:
Grasping at straws for ideas.
 

charlie b

Moderator
Staff member
Location
Seattle, WA
Occupation
Electrical Engineer
Re: Random tripping problem

Several thing come to my mind. One is the age of my mind, and the rest of my body to boot. Things get old, and then they don?t behave like you think they should. You might have to look into replacing the breakers, if replacements are even available (I would not know about that).

But there is another possibility that should not be discounted without some thought. Let me ask, how does this problem make itself known? What I mean is, does a breaker trip while someone is standing next to it and watching it? Or does something stop working, and then you look for the cause, and discover a breaker tripped? One very important question: is the breaker discovered to be in the ?off? position, or in the ?trip free? position, or has anybody made the effort to tell which of the two positions the breaker is in, or do you know what those terms mean? What I am getting at is the possibility of ?malicious mischief,? also known sometimes as ?vandalism.? Can you say, from what you have personally observed, and not just from what you heard someone else say, that this problem absolutely could not have been intentionally caused by a person?
 

hurk27

Senior Member
Re: Random tripping problem

I had this once on a 3ka service in a plant that made a fiber product. it turned out to be a bad phase connection at the service transformer that caused a intermittent loss of one phase. This would of course cause a very high single phase load because of all the motors.
Just a thought.

[ August 18, 2004, 12:33 AM: Message edited by: hurk27 ]
 

alan mcneil

Member
Location
Massachusetts
Re: Random tripping problem

The breaker was in the TRIPPED position.

About a year ago I was having the same problem with another breaker in the same MDP.

I was able to get a breaker from Westinghouse of that frame size.
The replacement breaker was a thermal-magnetic syle, it did not have the electronic trip mechanism feature; it has not tripped since.

The electric room is locked, I don't think it is vandalism since the breakers are always in the tripped position.
 

brian john

Senior Member
Location
Leesburg, VA
Re: Random tripping problem

The early generation of Westinghouse static tripmolded case circuit breakers have a problem with the OCP devices, sometimes it is just the rating plug other times it is the complete OCP device.
 

charlie tuna

Senior Member
Location
Florida
Re: Random tripping problem

i am assuming your facility has not added or changed anything and ran without tripping for some time and "now" different breakers are tripping for no apparent reason? you have an upstream switchgear problem---possibly a bad vault stub connection or main breaker connection problem---these breakers are sensing a single phase instantanious situation due to a bad connection on the phase that is bad. this single phase condition is causing the tripping---my guess! get a infrared thermographer to scan all connections upstream of the tripping area. if this is the case you might save alot of damage when this connection finally opens up!
 

catchtwentytwo

Senior Member
Re: Random tripping problem

I suspect something has changed in the system. Knowing all the functions available on the trip unit should be useful.
 

alan mcneil

Member
Location
Massachusetts
Re: Random tripping problem

The only adjustments are X2 X5 and X10 of instantaneous trip.

Weeks or even months will pass without a trip, then for no apparent reason it will trip.

I suspect that the circuit board (circa 1970) cannot distiguish strange frequencies running through the system and a fault.

What has changed is digital technology (VFDs computers scanners etc.)

The total harmonic distortion is around 2 or 3 percent, nothing to worry about....yet.

I was just wondering if there is any documentation stating this problem, I hear alot of rumors but nothing solid at this point in time.
 

catchtwentytwo

Senior Member
Re: Random tripping problem

Have you tried contacting Westinghouse? I realize that Cutler-Hammer bought them out but it would be worth separately trying a sales office and/or the field service organization (if one exists). I've found there sometimes is a "don't tell if they don't ask" code of silence from manufacturers concerning this stuff. When confronted, a field service bulletin may "appear".

If you can find a independent breaker service/rebuilding/testing shop, they might be a good source of advise. The International Electrical Testing Association is a good place to find some http://www.netaworld.org/

Finally try a Google or Yahoo search with variants of the product and problem.
 

ken987

Senior Member
Re: Random tripping problem

I've ran into this at a local school we serviced we handled the hvac and the electrical needs. All FPE breakers all about 30yrs old this one was a 277/480 300 amp breaker for a roof top. The lugs for the wires were tight, however upon further inpection, touching the middle phase wire resulted in a burn. Why? Lugs were tight for the wire, lug connected to breaker was not. Your breaker may have a same problem. Right after one trips check for exessive heat, at lugs and wires. We have had a few breakers at this location do this.
 

alan mcneil

Member
Location
Massachusetts
Re: Random tripping problem

That is one of the first things I check,this is a strange problem with no simple answers.
I will keep looking and reading, I will solve the problem one of these days. :roll:
 

charlie tuna

Senior Member
Location
Florida
Re: Random tripping problem

i have had the same problems on various installations. one building had a problem where one of the chillers just went "off" line? then a few days later--a different chiller? this went on for near two weeks, then breakers off this same feeder began tripping? it was caused by a poor bus duct feeder joint on 4000 amp bus!

when a load of 25 or 30 per cent of the breaker's capacity trips it points to a single phase problem. if the load is up around eighty per cent, then there's a possibility that a branch load is causing it. my .02 cents
 

alan mcneil

Member
Location
Massachusetts
Re: Random tripping problem

Thank you all, and Thank you Charlie Tuna.
I have someone coming in next week to do some therm readings and we will take a close look at all of the buss in that board.
 

hurk27

Senior Member
Re: Random tripping problem

Alen
This bad connection could be any where in or before this panel all the way to the transformer, as I posted before. so don't stop just at that panel as all connections should be checked while you have the therm scope there.
 

charlie tuna

Senior Member
Location
Florida
Re: Random tripping problem

allen,
look at everything back and including the service--possible prblem in the vault on the power company's side??? if it's bus duct--all the joints! if it's cable all the connections!
 
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