A client recently had a conductor short to ground on a 3 phase supply to a transformer. It is supplying 480/277 to 120/208 3 phase 75kva transformer. There are no 3 phase loads but there are 208v electric heaters and 120v receptacles for general use power. Unfortunately where this is located it will be a couple of weeks before the repair can take place. I'm trying to think of a way to get some sort of temporary power restored until I can repair the conduit and pull wire. Does anyone have experience on phase loss on the primary of a transformer, and what can I expect to see?
480/277 Single phase to 208/120
- Thread starter pitkas
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kwired
Electron manager
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- NE Nebraska
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- EC
Is transformer primary delta?
Is fault in the supply conductors or in the transformer?
Not sure how well delta-wye will operate if only supplied with single phase, but I think you can still get two phases out of the secondary.
I do know POCO wye-wye pole top banks work fine with a lost primary conductor - but you only get two secondary phases.
wye-delta - if not too heavily loaded, you won't even know you lost a primary phase and three phase secondary loads still work - it essentially becomes an open delta primary when that happens.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
After further thinking - if you have delta primary and lost incoming A - that only leaves you full voltage across B-C. You would get back feed from B-A and C-A - should be half normal voltage across those if secondary were unloaded.
This should leave you with only one line to neutral on secondary with normal voltage I think, others will be reduced voltage.
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