8.1. A 60 Hz alternating voltage having an RMS value of 100 V is applied to a series RL circuit by closing a switch. The resistance is 15 and the inductance is 0.12 H.

a. Find the value of the DC component of current upon closing the switch if the instantaneous value of the voltage is 50 V at that time.

b. What is the instantaneous value of the voltage that will produce the maximum DC component of current upon closing the switch?

c. What is the instantaneous value of the voltage that will result in the absence of any DC component of current upon closing the switch?

d. If the switch is closed when the instantaneous voltage is zero, find the instantaneous current 0.5, 1.5, and 5.5 cycles later.

8.2. A generator connected through a 5-cycle circuit breaker to a transformer is rated 100 MVA, 18 kV, with reactances of x"d = 19%, X'd= 26%, and Xd = 130%. It is operating at no load and rated voltage when a three-phase short circuit occurs between the breaker and the transformer. Find (a) the sustained short-circuit current in the breaker, (b) the initial symmetrical RMS current in the breaker, and (c) the maximum possible DC component of the short-circuit current in the breaker.

8.3. The three-phase transformer connected to the generator described in Problem 8.2 is rated 100 MVA, 240Y/18Δ KV, X = 10%. If a three-phase short circuit occurs on the highvoltage side of the transformer at rated voltage and no load, find (a) the initial symmetrical RMS current in the transformer windings on the high-voltage side and (b) the initial symmetrical RMS current in the line on the low-voltage side.

8.4. A 60-Hz generator is rated 500 MVA, 20 kV, with x"d = 0.20 per unit. It supplies a purely resistive load of 400 MW at 20 kV. The load is connected directly across the terminals of the generator. If all three phases of the load are short-circuited simultaneously, find the initial symmetrical RMS current in the generator in per unit on a base of 500 MVA, 20 kV.

8.5. A generator is connected through a transformer to a synchronous motor. Reduced to the same base, the per-unit subtransient reactances of the generator and motor are 0.15 and 0.35, respectively, and the leakage reactance of the transformer is 0.10 per unit. A three phase fault occurs at the terminals of the motor when the terminal voltage of the generator is 0.9 per unit and the output current of the generator is 1.0 per unit at 0.8 power factor leading. Find the subtransient current in per unit in the fault, in the generator, and in the motor. Use the terminal voltage of the generator as the reference phasor and obtain the solution (a) by computing the voltages behind subtransient reactance in the generator and motor and (b) by using Thévenin's theorem.

8.6 Write a summary report and rough calculation of your own solution to connecting the global with an intergrid electrical energy, provide a rough estimate.