Transformer protection

[garyevans76]

I am installing a 175 kva transformer but only need 80 amps on the secondary. Can I protect the primary at 200 amp? It is three phase

 

[GoldDigger]

What are the voltages?

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[petersonra]

Is this a Delta Delta Transformer where you are trying to avoid putting secondary protection in

 

[garyevans76]

transformer protection

transformer protection

It is 208Y to 400Y

 

[garyevans76]

transformer protection

transformer protection

I only have 200 amps available on the primary

 

[augie47]

Given the specs on the transformer and breaker, an engineer could confirm but I have serious doubt a 200 amp breaker will handle the inrush current of a 175kva @ 208.

 

[augie47]

Sure about the kva ? 175 is an odd size.

 

[garyevans76]

yes it is 175 KVA it is an odd transformer

 

[GoldDigger]

I only have 200 amps available on the primary

Only 200A available by load calculations or by upstream OCPD?
If the former, you can put a larger breaker on the primary to handle inrush and use a breaker on the secondary to limit the load.
If the latter, you simply may not be able to use that transformer.

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[electrofelon]

This is not really a good design. You have three times the transformer you need which may equate to more losses. Also as has been mentioned, starting it may be an issue. I think it will start but you may have to try several times. Now this maybe may not be that big a deal depending on a variety of factors such as how often it is energized, the type of load, whether it is on an ats, the knowledge and qualifications of people using it, etc.

 

[Besoeker]

Given the specs on the transformer and breaker, an engineer could confirm but I have serious doubt a 200 amp breaker will handle the inrush current of a 175kva @ 208.

I'm inclined to agree. Unless some kind of current limiting like a soft start is used.

 

[JFletcher]

With 400 volt 3 phase, I guess you are running a european-spec motor of some kind? What is the load, and what are the specifications of that load?

With 80 amps on the secondary, your primary is going to run about 157 amps or so.