No load test of 5 MVA transformer 33kV/11kV

[Irangi]

Hi,
When we doing no load test for newly built transformer it was found that we can not supply balance voltage to the input side. We are feeding from MG set through 250kVA 33/415 small transformer to 33kV side of 5 MVA transformer. when we increase the voltage supply voltage show phase unbalance. What will be the possible causes? If need more information please let me know. We did induced over-voltage test and transformer withstood it. Then there cant be any issue in winding. Results of the some other test we carried out were attached. Why this unbalance comes?

 

[prc]

Did you ground the neutral of source and 250 KVA transformer neutral. What are the vector connections of250 KVA and 5 MVA Transformers ?

 

[Irangi]

Hi, Both are Dyn11 and neutral of Gen and the 250kVA tf are earthed.

 

[Irangi]

Can design flux density (1.72 T) can cause this ? I meant is this flux density is too high?