Current at PE wire on the primary side of the transformer

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mohamed.hashim

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We have a step down transformer whose rating is 7.5kVA 690/230V . we found enormous current on PE wire at the primary side of the transformer, irrespective of load is connected or disconnected on the secondary side.

What would be the issue?
 
mohamed.hashim said:
We have a step down transformer whose rating is 7.5kVA 690/230V . we found enormous current on PE wire at the primary side of the transformer, irrespective of load is connected or disconnected on the secondary side.

What would be the issue?
Click to expand...

how much is enormous?

by PE do you mean what we would in the US call an equipment grounding conductor or a grounding electrode conductor?
 
mohamed.hashim said:
40 amps. it's equipment grounding conductor
Click to expand...

If the grounded conductor is bonded to the PE at some point, my first guess would be that the grounded conductor on the primary side is compromised in some way, forcing current through the PE. But in that case I would also expect the current to be even higher when a load is placed on the secondary.
 
When primary side circuit breaker is disconnected, current becomes zero.

See the attached picture.
 

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Transformer has both primary and secondary grounding connection. I haven't shown in the picture on the secondary side.

Primary side PE connection is connected to the PE terminal block which has a link to the metal base plate .. this baseplate again connected to the grounding.

Only issue is we see more current in the primary PE wire. If we disconnect primary disconnect, zero current measured.

We see the same current exist during the secondary is loaded or unloaded condition.
 
My first guess would have been a shorted winding on the primary side.

But, that should have tripped the primary breaker and you never mentioned that happening.

is this something new?

have you meggered the xfmr?
 
petersonra said:
My first guess would have been a shorted winding on the primary side.

But, that should have tripped the primary breaker and you never mentioned that happening.
Click to expand...
Depends on just where along the primary winding a short to the PE shield is located. If it was at a point which was close to earth potential, the current would be correspondingly small, and because of the ground electrode resistance it would not have the same effect on primary current as a shorted turn would.
 
mohamed.hashim said:
When primary side circuit breaker is disconnected, current becomes zero.

See the attached picture.
Click to expand...

A WAG* but I would look at a neutral issue they MAY HAVE crossed connected neutrals and the current is returning to it's sources, through your PE/ EGC )equipment grounding conductor).

*Wild A** Guess
 
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