Ans. One whose armature has, in addition to the main winding, another winding connected to a commutator for furnishing direct field exciting current, as shown in fig. 1,430.
Fig. 1,431.—Frame, bed plate and armature winding for Westinghouse bracket bearing polyphase alternator.
Ques. How is a direct connected exciter arranged?
Ans. The exciter armature is mounted on the shaft of the alternator close to the spider hub, or in some cases at a distance sufficient to permit a pedestal and bearing to be mounted between the exciter and hub. In other designs the exciter is placed between the bearing and hub.
Figs. 1,432 and 1,433 are examples of direct connected exciter alternators, in fig. 1,432 the exciter being placed between the field hub and bearing, and in fig. 1,433, beyond the bearing.
Ques. What is the advantage of a direct connected exciter?
Ans. Economy of space.
This is apparent by comparing figs. 1,432 and 1,433 with fig. 1,434, which shows a belted exciter.