1. EE 740 Professor Ali Keyhani Lecture #5 Three Phase Transformer Connections and Phase Shift

2. 13.2 kV127 kV T1 T2 = T1 T3 = T1 300 MVA Y-Y 219.71/22.83 kV

3. 300 MVA Y-Y 219.71/22.83 kV j16.129 3-phase Eqt. Ckt. j16.129 100 MVA 127/13.2 kV 10% 1-phase Eqt. Ckt. HVLV j.10 Per-unit Eqt. Ckt.

4. 13.2 kV127 kV T1 T2 = T1 T3 = T1 300 MVA Y-Y 219.71/13.2 kV

6. X3H3 X2 X1H1 H2 IcIc ICIC IbIb IBIB IaIa IAIA V AN V CN V BN V cn V bn V an ++ ++ ++ - - -- -- C A B c b a (a) Core and coil arrangments H1H1 H2H2 H3H3 X1X1 X2X2 X3X3 N n Ia IAIA IBIB ICIC IbIc Van V AN + + - - (b) Schematic representation showing phasor relationship for positive-sequence operation nN © Single-line diagram YY

8. X3H3 X2 X1H1 H2 C A B c b a (a) Core and coil arrangments N AN (Step 2) ba (Step 3) (Step 4) “a” connected to must be on the right side, and “b” on the left side of line a-b. A B C V AN N Step 1) Assume (+) sequence voltage 120 c b a n Van V AN 30 Step 2) Van is 30 behind V AN and abc sequence. Step 5) For (+) sequence V AN (HV) leads Van (LV) by 30.

10. X3H3 X2 X1H1 H2 C A B c b a (a) Core and coil arrangments N AN (Step 2) ba (Step 3) (Step 4) “a” connected to must be on the right side, and “b” on the left side of line a-b. A B C V AN N Step 1) Assume (-) sequence voltage 120 c b a n Van V AN 30 Step 2) Van is 30 ahead of V AN and acb sequence. Step 5) For (-) sequence V AN (HV) lags Van (LV) by 30. N