Feedback transformer used for slip power recovery system. In this Hv side 6.6KV and LV have two winding delta and Wye both output Phase to phase 413V. my question is when we supply 6.6KV and secondary make open. In this situation we found that line voltage is R-Y= 390, Y-B 393, B-R 393V. but phase to ground found R-E= 225V, B-E = 190, Y-E = 300 and neutral point of Wye ungrounded. While both LV open how?