SYNCHRONOUS GENERATORS 



291 



FIG. 162. Approximate Excitation of Water Wheel-driven Polyphase Syn- 

 chronous Generators. Per Kv.A. per R.P.M. Based on Maximum 

 Rating at 80 per cent Power Factor. 



Regulation. The regulation of an alternating-current gener- 

 ator is the rise in voltage when a specified load at specified power 

 factor is reduced to zero; the speed and field excitation remaining 

 constant. It is expressed in per cent of normal rated-load voltage, 

 and unless otherwise specified understood to refer to a non-induc- 

 tive load. 



A close inherent regulation was formerly considered one of 

 the essential requirements of a good generator, but fortunately 

 this idea is now entirely changed. A low percentage regulation 

 may be obtained in two ways; first, by designing the generator 

 with a field magnetically strong as compared with the armature, 

 so that the self-induction and demagnetizing effect of the armature 

 is comparatively small, resulting in a small increase in field current 

 required to maintain normal voltage with increase in load; and, 

 second, by saturating the magnetic circuit, particularly in the 

 field, where high densities do not increase the losses or temperature 

 rise. Both of these methods are, however, detrimental to the 

 present-day operating practice. A decrease in the synchronous 

 reactance, would proportionally increase the short-circuit currents 



