Hawkins Electrical Guide v. 07 (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. What effect is produced by poor contact of the primary relay?

Ans. It causes chattering in the secondary relay; which burns out and wears away its contact points, increasing the heating of the motor, creating objectionable noise and entailing wear and tear on the whole outfit.

Ques. Why does the movable contact arm of the primary relay tend to remain nearer one of the stationary contact points than the other?

Ans. This is due to the tendency of the relay to open the contact whenever the voltage equals that at which the contact closes.

Fig. 2,430.—Diagram of connections of automatic induction regulator and accessory apparatus on three phase feeder circuit.

Ques. What provision is made in the primary relay to prevent vibration or chattering?

Ans. Two auxiliary windings are provided: one in series with each of the stationary contact points and so arranged as to assist in making the contact by increasing the pressure on the contact points at the instant of closure.

The best effect of the compounding action of the auxiliary coils is obtainable when arranged for ¾ per cent. of the torque of the main coil.