. Hawkins electrical guide. Questions, answers & illustrations; a progressive course of study for engineers, electricians, students and those desiring to acquire a working knowledge of electricity and its applications; a practical treatise. iver momentarily arange from 25 to 160 volts at its armature terminals. It is obvious from the above that an exciter suitable for use with anautomatic regulator must commutate successfully over a wide range involtage, and, if properly designed, have liberal margins in its shuntfields and magnetic circuits. Alternator fields designed for and operated at unit
. Hawkins electrical guide. Questions, answers & illustrations; a progressive course of study for engineers, electricians, students and those desiring to acquire a working knowledge of electricity and its applications; a practical treatise. iver momentarily arange from 25 to 160 volts at its armature terminals. It is obvious from the above that an exciter suitable for use with anautomatic regulator must commutate successfully over a wide range involtage, and, if properly designed, have liberal margins in its shuntfields and magnetic circuits. Alternator fields designed for and operated at unity power factorhave often proved unsatisfactory when the machines were called uponto deliver their rated kva. at .8 power factor or lower. This is due tothe increased field current required at the latter condition and results,first, in the overheating of the fields and, second, in the necessity ofraising the direct current exciting voltage above 125 volts, which oftenrequires the purchase of new exciters. ALTERNATORS 1,169 Ques. What is a self-excited alternator? Ans. One whose armature has, in addition to the mainwinding, another winding connected to a commutator for fur-nishing direct field exciting current, as shown in fig. 1, Fig. 1,431.—Frame, bed plate and armature winding for Westinghouse bracket bearing poly«phase alternator. Ques. How is a direct connected exciter arranged? Ans. The exciter armature is mounted on the shaft of thealternator close to the spider huh, or in some cases at a distancesufficient to permit a pedestal and bearing to be mounted be-tween the exciter and hub. In other designs the exciter isplaced between the bearing and hub. 1,170 HAWKINS ELECTRICITY Figs. 1,432 and 1,433 are examples of direct connected exciter alter-nators, in fig. 1,432 the exciter being placed between the field huband bearing, and in fig. 1,431, beyond the bearing. Ques. What is the advantage of a direct connectedexciter? Ans. Economy of space. This is apparent by compar
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