Figure P5-3 shows a small industrial plant supplied by an external 480 V three-phase power supply. The plant includes three main loads as shown in the figure. Answer the following questions about the plant. The synchronous motor is rated at 100 hp, 460 V, and 0.8-PF-leading. The synchronous reactance is 1.1 pu and armature resistance is 0.01 pu. The OCC for this motor is shown in Figure P5-4.
(a) If the switch on the synchronous motor is open, how much real, reactive, and apparent power is being supplied to the plant? What is the current IL in the transmission line?
The switch is now closed and the synchronous motor is supplying rated power at rated power factor.
(b) What is the field current in the motor?
(c) What is the torque angle of the motor?
(c) What is the power factor of the motor?
(d) How much real, reactive, and apparent power is being supplied to the plant now? What is the current IL in the transmission line?
Now suppose that the field current is increased to 3.0 A.
(e) What is the real and reactive power supplied to the motor?
(f) What is the torque angle of the motor?
(g) What is the power factor of the motor?
(h) How much real, reactive, and apparent power is being supplied to the plant now? What is the current IL in the transmission line?
(i) How does the line current in part (d) compare to the line current in part (h)? Why?
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