Contactor failure 1

[Aexer]

Hi, let me get to the point right away, i recently was called to maintain a 160kva perkins generator with an ats that has two af 205-30 contractors for switching...and in my inspection one of the poles from the generator contactor has melted and so was not conducting at all, while the other two poles were working fine, along with the mains contactor,(i took a picture bzw). It would really be helpful if i had your insights as well,as the ats is new(only worked for three months), the load consists of an elevator with 600kg max, a 3hp pump, and lights for a house,( the generator controller did not trip any alarm which it would have done with overload and stuff. Can you help??

 

[waross]

Bad connection.
The bolt may have not been tight enough, the jumper may not have been properly cleaned of aluminum oxide before being connected, if the contactor has replaceable contacts, the contact may not have been fastened securely.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[ScottyUK]

Almost certainly as Bill says above - bad connection.

I don't think that contactor has field-replaceable poles, but you should be able to carefully dismantle it to have a look inside and check for problems. Look for simple things like fragments of foreign material preventing correct operation, either by jamming the moving yoke or by preventing full contact on the pole face.

 

[waross]

Good point Scotty. I have seen plastic contactor parts distorted by heat from a failure. I have also seen the full travel of a contactor compromised by foreign matter.

I have seen ATS contactors destroyed and contacts burnt off by closing in on too much load.
The load starts to stall the generator. As the speed drops the voltage drops. At some point the contactor drops out, pulling a heavy arc. With no load the set accelerates. The voltage builds up and the contactor re-closes. The cycle repeats. It only takes a few minutes to burn the contacts through to an open circuit.
I know of two instances and was able to avert the same problem in a lot of other installs.
When that happens, all contacts are damaged even if only one pole burns free.
In your instance, I am not sure of the load.
I have been looking for my old formula to convert 600 kg to KVA.
A couple of factors may be missing.
In any case, I doubt that it is enough to stall a 150 KVA set.

When replacing the contactor, remove the connecting jumper and clean it well of any corrosion. This includes both ends and the main bus where the jumper makes contact.

The screw fastening the jumper to the contactor may have been loose and started the failure sequence.
I have seen similar failures on circuit breakers.
Or maybe something else.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Aexer]

Thanks guys, its awesome to have ur insights