Breaker Failure on 1000HP drive unit

[toastedhead]

Here are some pics of the failure. What could cause this or what are some of the modes of failure?

Some information -
Its 480V main drive unit. The failure occurred on a model 140-R6 molded case circuit breaker.
The failure occurred on the line side between L2 and L3. The back of the input conductor was melted and the arc had actually melted and penetrated the sub panel.

 

[rcw retired EE]

No pictures came through. I don't recognize a 140-R6 breaker. Manufactuer? What is its rating 1600Amps, 1400 Amps?

Some possible causes:
1. Loose connection on incoming wire causing overheating and eventual arcing actoss phase-phase.
2. Foreign material shorting across the incoming terminals or between one terminal and grounded metal.
3. Dust or moisture shorting out the terminal to ground.
4. Animal shorting out leads.
5. Voltage surge from outside casuing an arc across the insulation.

Could be many other things.

 

[toastedhead]

Its an Allen Bradley Molded case breaker. I think its actually made by Cutler Hammer. Its mounted to a back plane inside of a VFD. Im surprised stuff could get behind it the way it is mounted to back plane.

 

[jraef]

Yes, it is a Series C Eaton R frame molded case breaker. Probably 1600A but a 2500A Frame

No pictures as rcwilson said, but in addition to what he mentioned what cable, size and quantity did you use for wiring the input (L2 and L3 means it was on the field connection side of the breaker) and how was it connected? Mechanical lugs, crimp lugs?

"Will work for (the memory of) salami"

 

[DRWeig]

Just a note -- I can see the pictures just fine. I'll help toastedhead out and attach a screen shot, I'm interested in learning how this one resolves.

Best to you,

Goober Dave

Haven't see the forum policies? Do so now: Forum Policies

 

[jraef]

So I can't tell from those pictures, but it almost looks as though either the bus connectors were loose, or someone tried to connect to the breaker without the proper accessory. Those pads are NOT the direct connection point you know, don't you?
Take a look at this cut sheet and let us know what terminating accessory was used, or if they maybe didn't use one.

"Will work for (the memory of) salami"

 

[toastedhead]

Those terminal blocks are exactly how they connected the wires.

Link

 

[ScottyUK]

Normally these breakers rely on the buswork acting as a heatsink to keep the temperature of the primary disconnects down to an acceptable temperature. I think jraef might have found the smoking gun - without the heatsink provided by the busbars it's pretty much inevitable that the breaker will overheat if it is loaded anywhere near to rating.

 

[jraef]

Not to mention that those pads being inset into the frame appear to possibly not allow the cable lugs to seat flat against them, which would create severe hot spots. They do that on PURPOSE as a way to signal to the installer that something is missing...

"Will work for (the memory of) salami"

 

[ScottyUK]

The grey bit between the ears perhaps...?

 

[jraef]

"Will work for (the memory of) salami"

 

[LionelHutz]

Since the proper termination kit was used, it would appear that wasn't the cause.

I don't see any signs of overheating damage that would be caused by loose connections.

My guess would be contamination of some sort.

Is that breaker supposed to have some kind of insulating paper used under it?

 

[living2learn]

Not to steal this thread but I saw this installation the same time I saw this thread and thought this installation was incorrect too. It uses DLO cable and this installation was not re-listed.

Sorry again if I stole your thread - no disreprect.

 

[toastedhead]

How much debris would it take to cause that arc to occur? There seems to be quite the void to fill up before debris could cause the arc?

Picture of aftermath

 

[LionelHutz]

It doesn't take much, one little drill shaving pigtail could cause that.

 

[toastedhead]

Wow Really? Seems like a pile would have to be built up between the back plane and the breaker body before an arc could be created.

Thanks for you help guys!

 

[ScottyUK]

Once the metal fragment is vapourised it forms a path of ionised gas and the arc current flows through the ionised gas. You don't need much metal. Switchgear arc containment tests typically use a bare copper wire wrapped between busbars as the ignition wire. I was surprised to see that the wire is only 1.5mm² or 2.5mm², but I've seen the result first hand at IPH in Berlin and frankly it's disturbing just how easy it is to start an arc.

 

[davidbeach]

That little wire doesn't even have to actually touch both bus bars, it only needs get close.