Fig. 1,432.—General Electric alternator with direct connected exciter mounted on shaft between field hub and bearing. In the smaller sizes, the magnet frame is bolted to the bearing bracket, but in the larger sizes special construction is used depending upon the conditions to be met. The exciters are capable of furnishing the desired excitation for low power factors.
Ques. What is the disadvantage of a direct connected exciter?
Ans. It must run at the same speed as the alternator, which is slower than desirable, hence the exciter must be larger for a given output than the gear driven type, because the latter can be run at high speed and accordingly be made proportionally smaller.
Ques. What form of gear is generally used on gear driven exciters?
Ans. Belt gear.
Fig. 1,433.—Fort Wayne alternator with direct connected exciter mounted on the field shaft at such distance as to permit a pedestal and bearing to be mounted between the exciter and revolving field. In the view, the bearing is hidden by the exciter, only the foot of the pedestal being visible.
Ques. What are the advantages of gear driven exciters?
Ans. Being geared to run at high speed, they are smaller and therefore less costly than direct connected exciters. In large plants containing a number of alternators one exciter may be used having sufficient capacity to excite all the alternators, and which can be located at any convenient place.