Derive, for both star- and delta-connected systems, an expression for the total power input for a balanced three-phase load in terms of line voltage, line current and power factor. The star-connected secondary of a transformer supplies a delta-connected motor taking a power of 90kW at a lagging power factor of 0.9. If the voltage between lines is 600V, calculate the current in the transformer winding and in the motor winding.

In an electrical system, each of the service entrance conductors has an area of 750 kcmil. The size of analuminum grounding conductor that will be brought to the service should beA. 250 kcmil.B. 4/0.C. 2/0.D. 500 kcmil

d) A regulator as shown in Figure 4 has an input voltage, Vs 12 V. The duty cycle, k = 0.35 and the switching frequency is 30 kHz. It also has an inductance, L= 200 µH, filter capacitance, C = 440 µF. The average load current, la = 1.25 A. Determine the; i. average output voltage, Va. ii. peak-to-peak output ripple voltage, AVc. iii. peak-to-peak output ripple current of inductor, AI. iv. peak current of the transistor, Ip. v. critical values of L and C. vi. critical values of L and C if Vs is increased to 14 V. Estimate the change in percentage for the critical values of L and C. V, Load V V G Figure 4