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

Special dynamos have been designed to overcome this objectionable feature, still this method of regulation is not extensively used.

Ques. What may be said of the third method of regulation?

Ans. The third method, that of variation of field strength, is the one in general use.

Ques. How is the field strength varied?

Ans. This may be done by the two path method, or by the variable field coil method.

Ques. Describe the two path method of field regulation.

Ans. An adjustable resistance or rheostat is connected in parallel with the field winding as shown in fig. 191. This shunts more or less of the current from the field winding according to the amount of resistance made active by the lever, L.

Thus, if the current in the armature and main circuit be 10 amperes and the resistance of the field winding 10 ohms, a resistance of 40 ohms in parallel with the winding would cause the current to split in the ratio of 40 to 10, or 4 to 1; 2 amperes would pass through the resistance and 8 amperes through the field.