Page 300 - Solutions Manual to accompany Electric Machinery Fundamentals

 Q   69.09 kvar 
PF  cos tan -1 TOT   cos tan  1   0.838 lagging


P TOT    105.9 kW 
The current supplied by the utility is
P 105.9 kW
I  TOT   152 A
L
3 V T PF 3 480 V 
 0.838
(b) With the switch closed, P 3 is added to the circuit. The real and reactive power of P 3 is

V 2  V 277 2
P  3  cos  3  cos -   90  0 kW
3
Z 5
V 2 277 V  2
P  3 3  sin  3 sin 90 -    46.06 kvar
Z 5 


P TOT  P  1 P  2 P  3 59.86 kW 46.04 kW 0 kW  105.9 kW


Q TOT  Q  1 Q  2 Q  3 34.56 kvar 34.53 kvar 46.06 kvar  23.03 kvar
The apparent power supplied by the utility is
S TOT  P TOT 2  Q TOT 2  108.4 kVA
The power factor supplied by the utility is

 Q   23.03 kVAR 

PF cos tan -1 TOT   cos tan  1   0.977 lagging


P TOT    105.9 kW 
The current supplied by the utility is
P 105.9 kW
I  L TOT   130.4 A
3 V T PF 3 480 V 
 0.977
(c) The total current supplied by the power system drops when the switch is closed because the
capacitor bank is supplying some of the reactive power being consumed by loads 1 and 2.

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