Step down transformer problems 3

[DanielB]

I'm moving (read moved)my woodworking business into what was a paper mill and is now being rented out to multiple businesses. The plant electrician is trying to get my 220 volt 3 phase properly set up. The building location I'm in has 3 step down transformers (560 to 220 volt) left from the days of paper making. The assumption was that I was all set. Not so.

When checked, the transformers were putting out proper voltage on two legs, but not on the third. The electrician employed by my landlord replaced the transformer that was apparently defective(2 days work), ------but now one of the other(!!) transformers is indicating low voltage output. The electrician has lots of experience with industrial electrical work but he seems stumped by this. He is now considering scavanging another transformer from another location in the mill (7.5 kvw instead of 10 as the others are). The engineer who has been doing consulting here is on leave or on vacation. I really wish he was available. Is there an obvious solution or answer to this situation? Anyone have any experience with this sort of thing? Is there anyone out there who'd be willing to talk with him?

Thanks
D. Bloomer

 

[resqcapt19]

Daniel,
When you checked voltage to ground, did you also check phase to phase voltage? In older buildings a 3 phase corner grounded system was sometimes used. In this system you would have 220 in all combinations of phase to phase, but only 2 phases would have voltage to ground.
Don(resqcapt19)

 

[gordonl]

Or it may be an ungrounded system with a ground fault.

 

[electricpete]

Are the primaries of the 3 transformers connected in delta or wye?

Are the secondaries of the 3 transformers connected in delta or wye?

Are any of the wye neutrals grounded?

Did you measure voltages from phase-to-ground or phase-to-phase? Did you check for proper voltage on the primary also (phase-to-ground?)

Was there load on the transformers at the time you took the measurements (prefer not to have load to help prove the problem is with the transformer)? If yes was it a balanced 3-phase load?

Did you check for fault on transformer output but by megger (transformer deenergized)?

Careful review of the above should be able to determine whether the problem is within TR or outside of it.

To check for problem within TR, numerous tests available. Megger, turns ratio, winding resistance being the easiest with inexpensive equipment. Also possible Doble test with magnetization current etc.