Chapter 3, Problem 3.56P

Three single-phase two-winding transformers, each rated $\text{3 kVA},\text{ 22}0/\text{11}0\text{ volts},\text{ 6}0\text{ Hz},$ with a 0.10 per-unit leakage reactance, are connected as a three-phase extended $\Delta$ autotransformer bank, as shown in Figure 3.36(c). The low-voltage $\Delta$ winding has a 110 volt rating. (a) Draw the positive-sequence phasor diagram and show that the high-voltage winding has a 479.5 volt rating. (b) A three-phase load connected to the low-voltage terminals absorbs 6 kW at 110 volts and at 0.8 power factor lagging. Draw the per-unit impedance diagram and calculate the voltage and current at the high-voltage terminals. Assume positive-sequence operation.