450.3(A) MV transformer protection

[jim dungar]

Makes sense.
But I think I still need a fused disconnect - maybe cutouts? - at least something to isolate each primary against inrush current. Without this all 3 2500kVA transformers will energize at the same time. Surely a single CB can’t handle this amount of current without nuisance trips.


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Even if you have protection at each transformer, the single feeder breaker will see all of the simultaneous inrush currents.

 

[Isaiah]

Even if you have protection at each transformer, the single feeder breaker will see all of the simultaneous inrush currents.

Yes but I can energize each transformer individually with a (fused) disconnect.


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[jim dungar]

Yes but I can energize each transformer individually with a (fused) disconnect.


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And what will happen when there is a momentary outage at the utility causing the transformers to reenergize all at the same time?

 

[Isaiah]

And what will happen when there is a momentary outage at the utility causing the transformers to reenergize all at the same time?

Then there may be a trip at the CB. But this would be infrequent


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