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# Transformer with Two Primary windings

## Transformer with Two Primary windings

(OP)
Hello,
I have a question regarding a functionally use for 3 winding transformer, and after long time that me and my collegue could’nt find and obtained a very demonstration, because the only answer that they gave to us was “the volt per turn must be the same”.
I think that you are the right persons to ask, because your knowledge.
The task is about three windings step-up transformer, with the feeding from two primary windings P1 & P2 by two generators.
I try to explain by and example:
NP1 = 70 turns
NP2 = 70 turns
VP1= 4000 V
VP2 = 4100 V (due to little differences of voltage generator)
In this way I’m feeding the transformer with two different volts per turns.
What happen in the transformer? It could be some problem?
We think that could be problem regarding circulating current between P1 and P2 windings, but we never find a real physic demostration.
Thank so much for attention
Best regards

### RE: Transformer with Two Primary windings

"...two generators..."

Phase locked?

If not, yikes.

### RE: Transformer with Two Primary windings

It's about the same situation as when two (or more) generators are feeding one line.
One transformer with two primary windings needs attention to load sharing and is not such a good idea when it comes to redundancy. But doable.
The phase locking happens automagically.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

### RE: Transformer with Two Primary windings

The result will be the same whether the generators are tied together directly, by two windings on one transformer or by two separate transformers.
Unequal voltages will result in a circulating reactive current limited by the impedance of the current path(s). One generator will be producing VARs and the other generator will be absorbing VARs.
There will be no direct effect on load sharing.
Load sharing is dependent only on the power supplied to each generator. This may be the throttle setting on a diesel generator or the steam flow control on a steam turbine generator.

Bill
--------------------
"Why not the best?"
Jimmy Carter

### RE: Transformer with Two Primary windings

(OP)
but in the transformer core what is the volt per turns that will be instituted?
In my example one windings imposes 4000/70 volt per turns and the other imposes 4100/70 volt per turns, I have to calculate the magnetic flux in the core.

### RE: Transformer with Two Primary windings

(OP)
No isn't for school,
thanks

### RE: Transformer with Two Primary windings

You will have a heavy reactive current flowing. The voltage drops associated with the heavy reactive current will cause the actual Volts per turn to be equal.
Volts per turn is related to the back EMF.
When two different voltages are connected together, reactive currents flow. The reactive currents are limited by the impedance of any transformers or generators in which the current flows.
When a system is presenting a KVAR demand to parallel generators, the sharing of the KVARs between the generators may be shifted by adjusting the voltages of the generators.
We don't generally confuse this well known effect with reference to Volts per turn.

Bill
--------------------
"Why not the best?"
Jimmy Carter

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