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1.  Junior Member
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Jan 2016
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Reputation During the performance of an excitation current test on a power transformer, you notice that two of the currents are higher than the third reading. Why? 2.  Junior Member
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Jan 2016
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Reputation  Originally Posted by kcorpuz During the performance of an excitation current test on a power transformer, you notice that two of the currents are higher than the third reading. Why?
It is due to transformer core reluctance which is proportional to current. Voltage that you apply for testing is constant therefore magnetic flux.
E(voltage) = 4.44 f*N(number of turns)*F(flux)
Voltage must be constant to keep Flux constant. Number of turns is fixed.

Now, N(number of turns)*I(current) = F(flux)*R(core reluctance)

Higher reluctance then higher current and opposite. Reluctance is lower for the center leg of transformer therefore current is lower. Two legs (one on each side) have higher reluctance and therefore have higher current value.
Last edited by Artonic; October 29, 2018 at 06:27 AM. 3.  Junior Member
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Reputation  Originally Posted by Artonic It is due to transformer core reluctance which is proportional to current. Voltage that you apply for testing is constant therefore magnetic flux.
E(voltage) = 4.44 f*N(number of turns)*F(flux)
Voltage must be constant to keep Flux constant. Number of turns is fixed.

Now, N(number of turns)*I(current) = F(flux)*R(core reluctance)

Higher reluctance then higher current and opposite. Reluctance is lower for the center leg of transformer therefore current is lower. Two legs (one on each side) have higher reluctance and therefore have higher current value.
Thank you the respond. That for sure helps a lot. 4.  Junior Member
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Jun 2022
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Reputation Hello,

I noticed that this is only true for a wye connected transformer, but not a delta connected transformer. Can anyone explain why this is? electrical drawings, electrical theory, neta exam questions, test procedures, transformers  