Page 157 - Solutions Manual to accompany Electric Machinery Fundamentals

(a) This machine is a generator supplying real power to the power system, because E is ahead of V .
A 
It is consuming reactive power because E cos  V .
A 
(b) This machine is acting as a generator, and the current flow in these conditions is

 

E  V 430 15  440 0 V


I  A    28.4 16.8 A
R  A A jX S 0.3 j 4.0
The real power supplied by this machine is


P  3V I A  cos   3 440 V 28.4 A cos  16.8   35.9 kW

The reactive power supplied by this machine is


Q  3V I A sin   3 440 V 28.4 A sin  16.8     10.8 kVAR

In other words, this machine is consuming reactive power.
(c) This machine is a motor consuming real power from the power system, because E is behind V .
A 
It is supplying reactive power because E cos  V .
A 
(d) This machine is acting as a motor, and the current flow in these conditions is

V  E 440 0 V 470  20



I   A   40.1 4.9 A
R  A A jX S 0.3 j 4.0
The real power consumed by this machine is

P  3V I A cos   3 440 V 40.1 A cos 4.9    52.7 kW

The reactive power supplied by this machine is

Q  3V I A  sin   3 440 V 40.1 A sin 4.9    4.5 kVAR

In other words, this machine is supplying reactive power. It is operating within its rating limits.

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