SYNCHRONOUS MOTORS IN LOCAL DISTRIBUTION 57 



power-factor. The disadvantages of low power-factor 

 were exhibited in a striking manner when induction mo- 

 tors became common and the load power-factor was re- 

 duced. The capacity of all the electrical apparatus for 

 delivering a certain power load, on which the income 

 depended, was reduced in proportion to the power-factor. 

 This applied to the generators, exciters, transformers, 

 and line conductors. It was also found that the prime 

 movers, such as steam-engines or water-wheels, were 

 out of proportion to the electrical machinery when the 

 power-factor was low. Thus it was impossible to load 

 the prime movers to their full capacity without overload- 

 ing the electrical apparatus. Therefore, in small power 

 systems, sending power only to short distances, synchro- 

 nous motors are useful more as power-factor correctors 

 than as voltage regulators. 



The simplest method of charging for electric energy, 

 namely, merely on a Kw.-hour rate, is liable to result 

 in low power-factor loads. The natural tendency where 

 there is no contract obligation to maintain a high power- 

 factor is to install induction motors of larger sizes than 

 are necessary, whereas by taking pains in measuring 

 the loads, the motors could be loaded more fully 

 with safety, and a higher power-factor would result. 

 When direct current is required, it will probably be 

 found that an induction motor-generator set or a synchro- 

 nous converter will be less expensive than a synchronous 

 motor-generator set, though the latter can give the most 

 power-factor correction. 



A common form of contract for the sale of electric 

 energy is one which gives a bonus to the customer when 

 the power-factor under load conditions is above, say, 



