Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

motor control circuit
a circuit containing devices such as the start/stop switches, mainline coil, main-line sealing contacts, overload contacts, timers and timer contacts, limit switches, antiplugging devices, and anything else used to control devices in the motor circuit.
motor current signature
analysis the use of the currents of an electric machine to provide diagnostic or other information on the health of the machine, coupling, or load.
motor operated switch
a switch operated by a motor that is capable of being controlled from a remote location.
motor starter
an electric controller, either manual or automatic, for accelerating a motor from rest to normal speed and for stopping the motor.
motor-generator set
a set consisting of a motor mechanically coupled to and driving one or more generators. The set used to be employed for AC-to-DC or DC-to-AC power conversion or voltage level or frequency conversion. Solid-state conversion units are replacing motor-generator sets in most applications.
multispeed motor
a motor that can be operated at any one of two or more definite speeds. For DC and induction motors, the speed settings are practically independent of the load, although the speed may vary with load for certain types of motors. Multispeed induction motors typically have two or more sets of windings on the stator with a different number of poles, one of which is excited at any given time.
permanent magnet AC motor
a generic term used to describe both permanent magnet synchronous motors and brushless DC motors.
permanent magnet DC motor

See permanent magnet DC machine
permanent magnet stepper motor
a stepper motor that has a permanent magnet assembly on the rotor.
permanent split-capacitor (PSC) motor
an induction motor that operates from a single-phase supply. The motor contains two phase windings in quadrature; however, one of them has a capacitor in series with it to create a phase shift between the winding currents. Both windings and the capacitor operate continuously so the machine acts like a two-phase machine when running at its operating speed, producing less vibration and noise than a single-phase motor. Since the capacitor runs continuously, it is sized smaller than the capacitor used in a capacitor-start induction motor (CSIM). Thus, the PSC motor produces a lower starting torque than the CSIM.
PSC motor

See permanent split-capacitor motor
reduced-voltage motor starter
a device designed to safely connect an electric motor to the power source while limiting the magnitude of its starting current. Various electromechanical configurations may be used: primary resistor, delta-wye, part-winding (requires special motor or dual voltage windings). Power electronic devices may also be utilized to gradually increase the applied voltage to system levels. The complete starter must also include fault and overload protection.
reluctance motor
a motor constructed on the principle of varying reluctance of the air gap as a function of the rotor position with respect to the stator coil axis. The torque in these motors arises from the tendency of the rotor to align itself in the minimum reluctance position along the length of the air gap.
repulsion-induction motor
a single-phase motor designed to start as a repulsion motor, then run as an induction motor. The rotor has a DC-type winding with brushes shorted together, in addition to the normal squirrel cage winding. Although it is an expensive design, it provides excellent starting torque with low starting current (similar to a universal motor) and relatively constant speed under load.
reversing motor starter
a motor controller capable of accelerating a motor from rest to normal speed in either direction of rotation. Some reversing motor starters can go directly from forward to reverse (or vice versa), while others must be stopped before a reversal of direction can take place. Both electromechanical and electronic reversing starters are available.
shaded-pole motor
a single-phase induction type motor that uses shaded poles on the stator to create a weak quasi-rotating magnetic field. Shaded-pole motors are only built in small fractional horsepower sizes and produce a very low starting torque that is suitable only for fan-type loads. See also shaded pole.
slotless motor
permanent magnet brush-less DC motor in which stator teeth are removed and the resulting space is partially filled with copper. The slotless construction permits an increase in rotor diameter within the same frame size, or alternatively an increase in electric loading without a corresponding increase in current density.
squirrel-cage induction motor
an induction motor in which the secondary circuit (on the rotor) consists of bars, short-circuited by end rings. This forms a squirrel cage conductor structure, which is disposed in slots in the rotor core.
See cage-rotor induction motor
synchronous motor
an AC motor in which the average speed of normal operation is exactly proportional to the frequency to which it is connected. A synchronous motor generally has rotating field poles that are excited by DC.
synchronous reluctance motor
a synchronous motor that depends on a reluctance variation on the rotor for the mechanism of torque production. The rotor shape is designed to provide a high difference in the reluctances between the d and q axes.
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