Contactor explosion - GE Limitamp IC 2814
Contactor explosion - GE Limitamp IC 2814
(OP)
Need ideas as to how this contactor blew up. GE Limitamp IC 2814 circa 1977. No operating data (jogging etc) available other than weather was clear. Services 2400V 450 HP pump motor. Coil is original AC type and appears to be in good shape though resistance is low (0.1 ohm). Were explosions like this the reason GE converted their coils to DC operation later? As you can see it blew a hole through the door and not much left of the guts to pinpoint failure. Any ideas as to history of failures and/or reasons would be appreciated. Thanks.
[IMG]http://i12.tinypic.com/348p0me.jpg[/IMG]
[IMG]http://i12.tinypic.com/348p0me.jpg[/IMG]





RE: Contactor explosion - GE Limitamp IC 2814
Is the system solidly grounded or grounded via an impedance?
My best guess is that something (tracking, dirt, insulation failure, rodent) initiated an arcing ground fault that escalated to a three-phase arcing fault.
What cleared the fault?
RE: Contactor explosion - GE Limitamp IC 2814
That all said, I sincerely hope no-one was hurt by the incident, and here's my best guess of what happened:
First, I think you had a contactor meltdown, which is closer to burning than exploding.
One cause of contactor meltdown is it's contacts arcing excessively while making or breaking. The extra arcing can occur for several reasons, I list 3 of the most common reasons I have encountered below:
1) weak coil voltage
2) mechanically the contacts don't pull in and release quickly enough due to binding or dirt in the mechanism
3) contacts are extremely "pitted" and have exceeded useful life
I personally expect #3 in this application, because of the age of the contactor. However, if regular electrical maintainance has been performed which includes cleaning the assembly and replacing it's contacts, then I'd vote for #1.
I bet with all the experts on this forum we can find a hundred other possible causes, anybody else care to guess?
RE: Contactor explosion - GE Limitamp IC 2814
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Contactor explosion - GE Limitamp IC 2814
RE: Contactor explosion - GE Limitamp IC 2814
RE: Contactor explosion - GE Limitamp IC 2814
When was the last time these were cleaned or tested?
RE: Contactor explosion - GE Limitamp IC 2814
If this was an arc, there are million and one things that could have caused it.
RE: Contactor explosion - GE Limitamp IC 2814
That was an air-break contactor on a roll out truck assembly. Here is what it was. Maunal link for GE HV contactors
You will likely never know the exact cause, but the most common mistake on air-break contactors is a lack of maintenance. Dust / dirt / contaminants build up, temperature changes allow condensation, tracking occurs then flashover.
JRaef.com
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: Contactor explosion - GE Limitamp IC 2814
Presumably the whole board was stripped and cleaned? There will be a lot of carbon-rich deposits over the busbars, insulators and any bushings which could easily provoke a repeat incident.
If the fault was able to persist at a relatively low energy level for a long time, as seems likely from the photos, you might want to investigate your protection scheme a little further. Is the neutral impedance grounded? This would account for a relatively low current arc being able to persist, but would call into question the earth fault detection.
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Sometimes I only open my mouth to swap feet...
RE: Contactor explosion - GE Limitamp IC 2814
RE: Contactor explosion - GE Limitamp IC 2814
rybrk
RE: Contactor explosion - GE Limitamp IC 2814
The contacts on yours may have been degraded to a point where a poor connection was established on closure, consequently overheating and catastrophically failing.
RE: Contactor explosion - GE Limitamp IC 2814
RE: Contactor explosion - GE Limitamp IC 2814
RE: Contactor explosion - GE Limitamp IC 2814
RE: Contactor explosion - GE Limitamp IC 2814
A fairly common problem with these is degradation of the arc chute ceramic plates. I found one once with a chunk of ceramic wedged in the contact gap. It could easily have ended up looking like yours.
A contactor in good condition can fail if it is asked to interupt excessive current, like "bumping" a motor or having a trip during start, if the starting current exceeds the interrupting rating. You have not said what cleared the fault, but it obviously escallated past the contactor's fuses. Was there any trip indication on the motor controls?