Page 133 - Solutions Manual to accompany Electric Machinery Fundamentals

 P
}
I
A2
I V 
A1
jX I }  P
S A

E A1 E A2
Q  I sin 
A
(c) The magnitude of the line current will be

P 15.93 kW
I  L   50.0 A

3 V T PF   3 230 V 0.8 
5-4. A 2300-V 1000-hp 0.8-PF leading 60-Hz two-pole Y-connected synchronous motor has a synchronous
reactance of 2.5  and an armature resistance of 0.3 . At 60 Hz, its friction and windage losses are 30
kW, and its core losses are 20 kW. The field circuit has a dc voltage of 200 V, and the maximum I F is
10 A. The open-circuit characteristic of this motor is shown in Figure P5-1. Answer the following
questions about the motor, assuming that it is being supplied by an infinite bus.

(a) How much field current would be required to make this machine operate at unity power factor
when supplying full load?
(b) What is the motor’s efficiency at full load and unity power factor?

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