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Delta to Delta Step Up Transformer

2923 Views 4 Replies 5 Participants Last post by  Tsmil
I am looking at wiring a Delta to delta step up transformer. 30 KVA. 208 3 phase primary and 600 3 phase secondary. My question is how do you safely groung the transformer so that if you have a phase go to ground it will trip the three phase breaker on the primary side.
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The primary low side is protected by the feeder breaker and is most likely fed from a grounded system already.

The secondary high side you want to protect should have one phase grounded. This will give you 600V-to-ground on the remaining two phases. And you'll have what's called a corner-grounded delta.

You need to be careful about how you treat your grounded phase. I don't have the Good Book in front of me, but for one thing, you can't use fuses in your secondary overcurrent protection because your grounded-phase overcurrent protection needs to open all the remaining phases.
 
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