206 ELECTRICAL MACHINERY 



The three terms we shall use in connection with power are 

 apparent power, power and reactive power. 

 We have also 



Apparent power = E I ......... (41) 



= voltage X current. 

 Power =Ecos 4>X/ or EXl cos $ ..... (42) 



= (active voltage X current) or (voltage X active 

 current). 



Reactive power E sin (J>X/ or EXl sin <j> . (43) 



= (reactive voltage X current) or (volt- 

 age X reactive current.) 



Example. To illustrate these definitions and terms an 

 example is given. Suppose that a certain circuit carries a 

 current of 20 amperes when the impressed voltage is 100 

 volts and that the phase difference between the voltage 

 and current vectors is 37, e.i., <j> = 37. Now if 4> = 37 

 cos 4> = 0.8 and sin <j> = 0.6. 



Hence 



Voltage = 100 



Current = 20 



Active voltage = 100 X 0.8 = 80 



Reactive voltage =100X0.6 = 60 



Active current = 20X0.8 = 16 



Reactive current = 20X0.6 = 12 



Apparent power = 1 00 X 20 = 2000 volt-amperes 



Power = SOX 20 = 1600 watts 



= 100X16 = 1600 watts; 

 Reactive power = 60X20 = 1200 watts 



= 100X12 = 1200 watts. 



