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4-18
INDUCTION MOTORS are the most commonly used of all electric motors due to their simplicity
and low cost. Induction motors may be single-phase or multiphase. They do not require electrical rotor
connection. Split-phase motors with special starting windings, and shaded-pole motors, are types of
single-phase induction motors.
SYNCHRONOUS SPEED is the speed of stator field rotation. It is determined by the number of
poles and the frequency of the input voltage. Thus, for a given motor, synchronous speed is constant.
SLIP is the difference between actual rotor speed and the synchronous speed in induction motors.
Slip must exist for there to be torque at the rotor shaft.
ANSWERS TO QUESTIONS Q1. THROUGH Q13.
A1.
Series, synchronous, induction.
A2.
To power small appliances.
A3.
They operate on either ac or dc.
A4.
The number of phases in the applied voltage.
A5.
90º .
A6.
Number and location of field poles.
A7.
Constant speed required by some loads.
A8.
They are simple and inexpensive to make.
A9.
Slip.
A10.
Load.
A11.
Single-phase induction motor.
A12.
By using combinations of inductance and capacitance to apply out-of phase currents in starting
windings.
A13.
They have very weak starting torques.
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