Page 293 - Solutions Manual to accompany Electric Machinery Fundamentals

Appendix A: Review of Three-Phase Circuits

A-1. Three impedances of 4 + j3  are -connected and tied to a three-phase 208-V power line. Find I  , I L ,
P, Q, S, and the power factor of this load.
SOLUTION
I L

+
I  Z   3   4 j

240 V Z  Z 

-
Z




Here, V  L V   208 V , and Z  j 3   5 36.87  , so
4

V 208 V
I   Z    5   41.6 A
I  L   3I   3 41.6 A  72.05 A

V 2  208 V 2
P  3  cos  3 cos 36.87  20.77 kW
Z 5 
V 2  208 V 2
Q  3  sin  3 sin 36.87  15.58 kvar
Z 5 
S  P  2 Q  2 25.96 kVA

PF  cos   0.8 lagging
A-2. Figure PA-1 shows a three-phase power system with two loads. The -connected generator is producing
a line voltage of 480 V, and the line impedance is 0.09 + j0.16 . Load 1 is Y-connected, with a phase
impedance of 2.536.87°  and load 2 is -connected, with a phase impedance of 5-20° .

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