×

# transformer excitation current readings

###### Jump to latest post
1.  Junior Member
Join Date
Jan 2016
Posts
7
Reputation ## transformer excitation current readings

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?  Reply With Quote

2.  Junior Member
Join Date
Jan 2016
Posts
4
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.  Reply With Quote

3.  Junior Member
Join Date
Jan 2016
Posts
7
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.  Reply With Quote

4.  Junior Member
Join Date
Jun 2022
Posts
1
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?  Reply With Quote

#### Tags for this Thread

electrical drawings, electrical theory, neta exam questions, test procedures, transformers  