# Parallelling transformers with different turn ratio and rating.

Discussion in 'Homework Help' started by Shafeey, Jan 7, 2011.

1. ### Shafeey Thread Starter New Member

Dec 5, 2010
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I got stuck in a problem while solving the previous exam question for my course...

Two transformers with unequal turn ratio and unequal ratings are connected in parallel and have the same secondary voltage. How will the load be distributed between them? Hence find the circulating current.

I know how to find the circulating current when the secondary voltages are different. But how can there be a circulating current if the secondary voltage is same?
And I know about the load distribution being inversely proportional to the line impedance of the transformers, but what will be the change taking circulating current into account?

Dec 26, 2010
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The circulating current results from the paralleling of two secondary windings which have different open-circuit voltages. When the windings are connected together, the difference between their induced voltages drives a current around the circuit connecting them.

Since the equivalent impedance seen looking into a voltage transformer output is normally relatively small, only a slight voltage difference may be needed to drive a significant circulating current. With sufficient mismatch, this can produce a destructive overload, even with no external load connected.

3. ### Shafeey Thread Starter New Member

Dec 5, 2010
2
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Thank you Adjuster. But that was not my question. I need to know what happens for the given case when the secondary voltages are same and the turn ratio is different.