EXCITERS 



355 



be of sufficient size to take care not only of the weight of the 

 exciter armature, but also of the revolving element and water 

 thrust of the turbine. 



In the case of a vertical generator the direct-connected exciter 



FIG. 210. Vertical Water-wheel-driven Exciter, Showing Thrust 

 Bearing at Top. 



is usually carried by the thrust-bearing bracket, as shown in 

 Fig. 211. 



Arrangement and Connections. 1 The question always arises 

 whether direct-connected exciters should be provided for each 

 unit or whether a central supply source, consisting of as few units 

 as possible is preferable. Either arrangement has its advantages 

 and disadvantages. The great advantage in a water-wheel-driven 

 exciter arrangement lies in the fact that it is independent of the 

 A.C. system with its load and speed fluctuations. Two units are 

 then usually provided, either of which has a capacity to take care 

 of the entire excitation of the plant, thus providing a 100 per cent 



1 See also Voltage Regulation. 



