transformer bank
transformer bank
(OP)
Hi guy,
here's the problem,
We have 3 single phase transformer 150 kVA 14.4kV/600V Z=2% connected wye-delta
one transformer burned.
We cannot find a 150 kVA transformer, but can find a 167 kVA easily.
From my point of view, there's no problem to add a 167 kVA if we adjust the impedance.
Z(167 kva) = 167/150 * 2% = 2.23 %, the impedance must be close to this at 167 kVA (±10%), and we protect the bank as a 3x150=450 kVA transformer.
The transformer vendor said we cannot do this. I Am pretty sure we can. What do you think?
And a other thing, the new tranformer will probably have two tap at the secondary, so it can be 14.4kV/347V or 14.4kV/600V. The impedance that the manufacturer give is for the 600 V or 347 V? I'm not sure it's very clear on the nameplate.
Thank for your help
here's the problem,
We have 3 single phase transformer 150 kVA 14.4kV/600V Z=2% connected wye-delta
one transformer burned.
We cannot find a 150 kVA transformer, but can find a 167 kVA easily.
From my point of view, there's no problem to add a 167 kVA if we adjust the impedance.
Z(167 kva) = 167/150 * 2% = 2.23 %, the impedance must be close to this at 167 kVA (±10%), and we protect the bank as a 3x150=450 kVA transformer.
The transformer vendor said we cannot do this. I Am pretty sure we can. What do you think?
And a other thing, the new tranformer will probably have two tap at the secondary, so it can be 14.4kV/347V or 14.4kV/600V. The impedance that the manufacturer give is for the 600 V or 347 V? I'm not sure it's very clear on the nameplate.
Thank for your help






RE: transformer bank
With your voltage ratings, it sounds like you'll wind up with the capability to have either a 600 V delta or a 347 V delta. Is that what you want?
RE: transformer bank
The bank is presently connected as the picture attached.
We don't need 347 V, but all the transformer available in the next few days have a 347 and 600 V tap. So the 347 V tap will be floating. Since the transformer must have the same impedance as the other 2, i was wondering if the impedance on the nameplate is for the 600 V tap.
RE: transformer bank
RE: transformer bank
"Theory is when you know all and nothing works. Practice is when all works and nobody knows why. In this case we have put together theory and practice: nothing works... and nobody knows why! (Albert Einstein)
RE: transformer bank
BTW I know where you can find another similar transformer that was ordered by the General Manager without having the order vetted by anyone knowledgeable in transformer ratings.
It's been sitting unused for years because it's not worth paying the return freight to the US from an island in Central America. 347V suitable for 600V wye systems. Needed 600V
If the voltage IS correct, the impedance is probably acceptable.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: transformer bank
After talking back to the vendor, the transformer is 14.4kV/347 V without 600 V tap.
it won't work on the system since the 2 other transformers are really 14.4kV/600 V, without possibility of 347 V.
Since we have a hard time finding 14.4kV/600 V transformer quickly, we'll probably be force to change the complete bank for 3 transformer 14.4kV/347V
Thanks
RE: transformer bank
While your checking you load see if you can get by with a Y-open Delta. You only need two transformers for the open delta.
RE: transformer bank
Putting both transformer impedances on the same kVA base, I assumed.
"Theory is when you know all and nothing works. Practice is when all works and nobody knows why. In this case we have put together theory and practice: nothing works... and nobody knows why! (Albert Einstein)
RE: transformer bank
Adjust the impedance means to calculate the impedance of the 150 kVA tranformer on a 167 KVA basis (2% on a 150kVA basis equal 2.23 % on a 167kVA basis).
Operate in OPEN-Delta allow only 57.7% of the initial rating of the bank, it isn't enought for the load.
RE: transformer bank
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: transformer bank
Impedance matching is a concern when paralleling transformers, but these won't be in parallel.