Different TTR results on same transformer single phase vs three phase

[gnagy13]

Went to a customer site and tested a transformer. The transformer was re-wound by the OEM and tested at their facility and came back with good results. The transformer was then installed at the customer site where we came in to test it. We first tested it single phase TTR on each tap. H3-H1 tests had three taps that were ranging from 3%-11.5% out of tolerance. We then tested the transformer three phase TTR and all taps came back within tolerance. Wondering if anyone has experienced this issue or something similar, if so could you explain why this is the case? I was asked to research this and explain to the customer on what is happening. Any feedback will be helpful. Thanks

 

[oldfieldguy]

Scott (Tee) wound?

old field guy