Testing of Wiring Between Transformer and Switchgear

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jimdavis

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salt lake city, UT USA
Hi guys,

I'm currently working on an expansion project at a medical manufacturing facility. One aspect of the project included the addition of a new 480Y/277 volt 2500A switchgear fed from a new 12470 volt 2500kVA transformer. The switchgear is connected to the transformer with multiple parallel conductors which have already been terminated at both ends.

My question is this- is there a way to effectively test the wiring to ensure none of the guys doing the terminating have crossed any phases without disconnecting the transformer connection? It seems to me that any type of testing at this point would read through the transformer windings and show continuity between phases. Anybody have any ideas before I disconnect the transformer to meter the wires?
 
The resistance through the coils might be larger than the resistance of a close cross connection.
You could also apply a controlled low voltage/current to the primary.

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jimdavis said:
Hi guys,

I'm currently working on an expansion project at a medical manufacturing facility. One aspect of the project included the addition of a new 480Y/277 volt 2500A switchgear fed from a new 12470 volt 2500kVA transformer. The switchgear is connected to the transformer with multiple parallel conductors which have already been terminated at both ends.

My question is this- is there a way to effectively test the wiring to ensure none of the guys doing the terminating have crossed any phases without disconnecting the transformer connection? It seems to me that any type of testing at this point would read through the transformer windings and show continuity between phases. Anybody have any ideas before I disconnect the transformer to meter the wires?
Click to expand...


In my opinion if you do not trust the connections, then I would disconnect them, that is the best bet.
 
With this size of power and service involved, why wasn't it tested by the installer,
or an independant service. I've seen the POCO ring their stuff, and frankly would be surprised that the EC didn't do the same!

All this is usually handled in the construction contracts. Are you sure now that in fact some records don't already exist?
 
My company did the entire installation. The new transformer is fed from the facility's existing substation and MV switchgear. The MV cables were hi-pot tested at the time if installation. I was not very involved with that aspect of the project but my boss is now asking me to ensure that there are no crossed conductors in the parallel 480 volt wiring. He would prefer that I not have to disconnect the transformer but I think it's the best way.
 
Disconnecting at one end and talking them out is probably the cheapest, quickest and most positive way of confirming the connections were correct.

A surge tester for checking motor winding faults might be suitable but if you find an imbalance between phases, you'll still have to disconnect to further investigate. If you don't have a tester, it can be pricey to rent.

If the phases weren't color coded before, it would be a good thing to do while you are re-verifying the wiring.



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A digital low resistance ohmmeter might also be an option to make a quick check.


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jim - I don't have any additional help on your question. The answers you got are good. But I do have a curiousity question:
jimdavis said:
... new 480Y/277 volt 2500A switchgear fed from a new 12470 volt 2500kVA transformer. ...
Click to expand...
A 480Y, 2500kVA xfm has an FLA of 3000A. One would normally use 4000A switchgear (secondary main cb set for 3750A). How come the small switchgear?

I'm guessing the exact xfm/swg sizing didn't much matter to your question and you used convenient round numbers. But if the switchgear is small, I'd be curious why.

ice
 
I would agree that the switchgear seems small or the transformer oversized on this job. The project is a multi-million dollar expansion on an existing facility and my employer didn't do the engineering for this job so unfortunately I do not know the answer to your question.
 
jimdavis said:
I would agree that the switchgear seems small or the transformer oversized on this job. The project is a multi-million dollar expansion on an existing facility and my employer didn't do the engineering for this job so unfortunately I do not know the answer to your question.
Click to expand...

Thanks for responding. It's interesting - but mostly from a curiosity point. And certainly nothing I would ever recommend you ask. Sometimes the answers are embarassing.

ice
 
jtinge said:
A digital low resistance ohmmeter might also be an option to make a quick check.


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Click to expand...

I concur. I have used a Biddle DLRO on cables connected to a large LV generator where we found crossed cables between phases.
It really saved a lot of man hours in knowing which connections to disconnect to correct the problem.
 
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