360 



ELECTRICAL EQUIPMENT 



main field circuits, as well as their losses. The exciter sets (Fig. 

 215), receive their driving power normally from an entirely inde- 

 pendent source, consisting of two auxiliary water-wheel-driven 

 low-voltage alternators with their own individual direct-connected 

 exciters (Fig. 216). These alternators feed into a set of bus-bars, 

 to which the exciter motors are normally connected. Provision 

 is also made, however, so that the exciter sets can be fed from 

 the main bus. One step-down transformer is provided for each 



FIG. 215. Exciter Set for Generating Unit in Mississippi River Power Com- 

 pany's Plant at Keokuk. 



bus section and supply power to an auxiliary exciter bus which is 

 sectionalized in the same number of groups as the main bus. 

 Connection can also be established (not shown in diagram), in 

 case of emergency, with a storage battery which ordinarily is 

 used for the operation of the oil switches. 



Besides supplying power for the exciter sets, the auxiliary 

 alternators also supply power for the station service and lighting, 

 although provision is made so that it can also be taken from the 

 main bus. 



