3.8. Three identical 9-MVA, 7.2-kV/4.16-kV, single-phase transformers are con- nected in wye on the high-voltage side and delta on the low voltage side. The equivalent series impedance of each transformer referred to the high-voltage side is 0.12 + j0.82 N per phase. The transformer supplies a balanced three- phase load of 18 MVA, 0.8 power factor lagging at 4.16 kV. Determine the line-to-line voltage at the high-voltage terminals of the transformer.

A short transmission line connects a step-up transformer on the source side with a series impedance of j0.5 ohms (referred to the primary) to a step-down transformer on the load side with a series impedance of 50 ohms (referred to the primary). The turn ratio of the step-up transformer is 1:14 and a no-load primary voltage of 17 (line-to-line) kV. The step- down transformer has a turn ratio of 18:1 and it has a Y-connected, balanced load of 0.463 +j 0.0772 ohms connected to its secondary side. A capacitor bank of -j0.324 ohms is added parallel to the load. Assuming an ideal transmission line, the effective impedance (per phase) of the system seen by the source would be: O A. 0.292 + j0.375 O B. None of the other choices are correct O C. 0.584 + j0.750 O D.0.196 + j0.158 O E. 5.84 + j7.5

3. A non-ideal 1-phase transformer has turns ratio 5:1 with 120Vac primary.  The primary impedance is 1 + j1 Ohms, and the secondary impedance is 0.2 + j0.2 Ohms.  Assume the core impedance (R0 and X0) can be neglected.  A resistive load of 12 Ohms is connected to the secondary.   What is the primary current magnitude? What is the secondary voltage magnitude? What is the efficiency of this transformer with this load?

3.8. Three identical 9-MVA, 7.2-kV/4.16-kV, single-phase transformers are con- nected in wye on the high-voltage side and delta on the low voltage side. The equivalent series impedance of each transformer referred to the high-voltage side is 0.12 + j0.82 S per phase. The transformer supplies a balanced three- phase load of 18 MVA, 0.8 power factor lagging at 4.16 kV. Determine the line-to-line voltage at the high-voltage terminals of the transformer.