A rotating field may be obtained from single phase current by what is known as splitting the phase.
Fig. 1,858.—Switch end view of General Electric drawn shell type fractional horse power single phase motor.
Ques. Describe one method of splitting the phase.
Ans. The field of the motor is provided, in addition to the main single phase winding, with an auxiliary single phase winding, and the two windings are connected in parallel to the single phase supply mains with a resistance or a condenser placed in series with the single phase winding, as shown in diagram fig. 1,830, the two windings being displaced from each other on the armature about 90 magnetic degrees, just as in the ordinary two phase motor.
Ques. What is the construction of the two windings?
Ans. The main coils are of more turns than the auxiliary, being spread over more surface, and are heavier because they are for constant use; whereas the auxiliary coils are used only while starting.
Figs. 1,859 to 1,862.—Detail construction of clutch parts of General Electric drawn shell type fractional horse power single phase motor. The starting switch, which is assembled within the motor frame, consists essentially of three parts: a rotating member mounted on the armature and provided with two spring controlled pivoted levers in contact with an insulated collector ring.
Ques. What are the auxiliary coils sometimes called?