TABLE OF CONTENTS A. A. DIVONA
A. J. DOLAN
J. R. HENDERSHOT
The two most common types of electric motors are alternating current (ac) induction and direct current (dc) commutated shunt- or series-wound. All electric motor configurations except one type (reluctance brushless) convert electrical energy to mechanical energy from the magnetic flux linkage of their two magnetic circuits. One of these circuits is in the stator and the other is in the bearing-mounted rotor. This flux linkage between the two magnetic circuits produces a moment of force at the rotor radius that results in a torque on the motor shaft causing shaft rotation. The speed of the rotation times the torque equals the output power at the motor shaft. This is, of course, the power used to drive a pump.
The basic difference between these two types of electric motors has to do with their electrical power source. The first type has been historically powered by 60 cycle (Hz) alternating voltages direct from the public utility power grid (50 Hz in most of Europe and some other parts of the world). For this type of motor, the speed is determined by the number of magnetic poles designed in the motor and the alternating sinusoidal frequency of the voltage from the power grid. Methods have been developed to alter the speed of an ac motor with a fixed number of poles and a fixed line frequency (it is also possible to wind such...
