Hawkins Electrical Guide v. 01 (of 10) / 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

by N. Hawkins

Ques. Which is the more desirable?

Ans. Theoretically, the long shunt is preferable as being the more efficient; however, in practice, the gain is not very appreciable and the short shunt is generally used.

Ques. What may be said regarding the voltage in short, and long shunt machines?

Ans. In a short shunt machine, the shunt winding is subjected to a higher voltage than with a long shunt. The pressure applied through a shunt winding with a long shunt, for any particular load, is equal to the voltage at the brushes plus the drop in the series winding.

Ques. For what other service besides incandescent lighting are compound dynamos adapted?

Ans. They are employed in electric railway power stations where the load is very fluctuating.

Ques. What is the effect of a short circuit on a compound dynamo?

Ans. It overloads the machine, since the excessive current flowing through the series field tends to keep the voltage at its normal value.

Unless the line be automatically opened under such a condition either by a fuse or circuit breaker, the machine and its driving engine may be damaged. To avoid this danger fuses or automatic circuit breakers are employed.