INDUCTION GENERATORS 349 



capacity. For example, assume a system with a load of 8000 Kw. 

 0.80 P.F., and that it is desired to install an induction generator 

 having a capacity of 5000 Kw. 0.80 power factor. What would 

 the required capacity of the synchronous generators then be? 



The wattless components of the load and the induction gen- 

 erator which the synchronous generators must supply will be 6000 

 Kv.A. and 2650 Kv.A., respectively, and, as in addition they must 

 furnish the remaining energy of 3000 Kw. their capacity would 

 have to be 



Kv.A. = VSOOO^+SeSO 2 = 9150, 



thus almost twice that of the induction generator. A somewhat 

 larger generator could, therefore, carry the entire load without 

 any induction generator. 



For a higher power factor, however, the condition would be 

 different. If the power factor, for example, were 0.95 instead of 

 0.80 the total wattless Kv.A. to be supplied would only be 2600+ 

 2650 = 5250 and the capacity of the synchronous generators 



Kv.A. = V3000 2 +5250 2 = 6045. 



For low-power factors it is, therefore, not very advantageous to 

 use induction generators. 



Operation. When putting an induction generator into opera- 

 tion it is only necessary to bring it up to speed and close the switch. 

 Synchronizing is not needed inasmuch as the machine cannot 

 generate any e.m.f. until excited from the line, and when so excited 

 it will, of course be in phase. 



The first current rush is only exciting current because the load 

 cannot be picked up until the field is established. If the current 

 rush should be undesirably large it can readily be reduced by 

 inserting reactances when the machine is thrown on the circuit. 

 These coils can then be cut out as soon as a steady condition is 

 reached. 



When driven by governor-controlled water wheels, the speed 

 of the induction generator will drop slightly with the load, and 

 in order to divide the load properly it will be necessary for the 

 speed of the synchronous generators to drop still more. The 

 best method of operating induction generators is, therefore, to 

 drive them with wheels without governor control. In this manner 



