transformer excitation current readings

[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?

[Artonic]

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.

[kcorpuz]

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.

[mfults1996]

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?