The character of this field is either
- 1. Oscillating[3], or
- 2. Rotating,
according as single phase or polyphase current is used.
[3] NOTE.—"The word oscillating is becoming specialized in its application to those currents and fields whose oscillations are being damped out, as in electric 'oscillations.' But for this, we should have spoken of an oscillating field."—S. P. Thompson. The author believes the word oscillating, notwithstanding its other usage, best describes the single phase field, and should be here used.
Figs. 1,626 to 1,628.—General Electric base construction for polyphase induction motors. The base is made of cast iron. Adjusting gear is provided to slide the motor along the base as shown in the illustrations, the movement being from 6 to 12 inches according to size. With this design of base, motors are securely held in position under all conditions and may be run with an upward pull on the belt. Close fitting guides moving in an accurately machined slot on the base preserve a correct alignment of the motor when adjustment of the latter is required. The same base can be used whether the motor be supported from the wall or ceiling or located on the floor. A single adjusting screw is placed under the center line of the motor frame, which produces an even and balanced draw in either direction on all parts of the motor when the belt tension is altered. This screw can be located at either end of the base. The base can be omitted when the motor is direct connected or when provision for belt adjustment is not required.
Ques. Describe briefly the operation of a single phase motor.
Ans. A single phase current being supplied to the field magnets, an oscillating field is set up. A single phase motor is not self-starting; but when the armature has been set in motion by external means, the reaction between the magnetic field and the induced currents in the armature being no longer zero, a torque is produced tending to turn the armature.
The current flowing through the armature produces an alternating polarity such that the attraction between the unlike armature and field poles is always in one direction, thus producing the torque.