In most instances, the following information will help identify a motor:
1. Frame designation – (actual frame size in which the motor is built)
2. Horsepower, speed, design and enclosure
3. Voltage, frequency and number of phases of power supply.
4. Class of insulation and time rating
5.
Application
The characteristic of an electric circuit by which varying
current in it produces a varying magnetic field which causes voltages in the
same circuit or in a nearby circuit.
An induction motor is an alternating current motor in which
the primary winding on one member (usually the stator) is connected to the power
source and a secondary winding or a squirrel-cage secondary winding on the other
member (usually the rotor) carries the induced current. There is no physical electrical connection
to the secondary winding; its current is induced.
A load (flywheel, fan, etc.) which tends to cause the motor
shaft to continue to rotate after the power has been removed (stored kinetic
energy). If this continued rotation
cannot be tolerated, some mechanical or electrical braking means must be applied.
This application may require a special motor due to the energy required
to accelerate the inertia.
A material which tends to resist the flow of electric current (paper, glass, etc.). In a motor the insulation serves two basic functions:
1. Separates the various electrical components from one another.
2.
It protects itself and the electrical components from attack of contaminants
and other destructive forces.
Five specialized elements are used, which together constitute the motor’s INSULATION SYSTEM. The following are typical in an AC motor:
1. TURN-TO-TURN INSULATION between separate wires in each coil. Usually enamel to random wound coils of smaller motors – tape on “form wound” coils of larger motors.
2. PHASE-TO-PHASE INSULATION between adjacent coils in different phase groups. A separate sheet material on smaller motors – not required on form would coils because the tape also performs this function.
3. PHASE-TO-GROUND INSULATION between windings as a whole and the “ground” or metal part of the motor. A sheet material, such as the liner used in stator slots, provides both di-electric and mechanical protection.
4. SLOT WEDGE to hold conductors firmly in the slot.
5.
IMPREGNATION to bind all the other components together and fill in the
air space. A total impregnation, applied
in a fluid form and hardened, provides protection against contaminants.
Since there are various ambient temperature conditions a motor
might encounter and different temperature ranges within which motors run and
insulation is sensitive to temperature; motor insulation is classified by the
temperature ranges at which it can operate for a sustained period of time
A requirement of service that demands operation for alternate
intervals of (1) load and no load; or (2) load and rest; (3) load, no load and
rest; such alternative intervals being definitely specified.
An auxiliary set of field poles carrying armature current to
reduce the field flux caused by armature reaction in a DC motor.
An electronic device that converts fixed frequency and fixed
voltages to variable frequency and voltage.
Enables the user to electrically adjust the speed of an AC motor.
Losses due to current flowing in a conductor caused by resistance
(equals the current squared times the resistance).