1. Introduction: The Induction motor is a three phase AC motor and is the most widely used machine. Its characteristic features are-
- Simple and rugged construction
- Low cost and minimum maintenance
- High reliability and sufficiently high efficiency
- Needs no extra starting motor and need not be synchronized
An Induction motor has basically two parts – Stator and Rotor
The Stator is made up of a number of stampings with slots to carry three phase windings. It is wound for a definite number of poles. The windings are geometrically spaced 120 degrees apart. Two types of rotors are used in Induction motors - Squirrel-cage rotor and Wound rotor.
|All loads moved by electric
motors are really moved by magnetism. The purpose of
every component in a motor is to help harness, control,
and use magnetic force. When applying an AC drive system
it helps to remember you are actually applying magnets
to move a load. To move a load fast does not require
more magnets, you just move the magnets fast. To move a
heavier load or to decrease acceleration time
(accelerate faster) more magnets (more torque) are
needed. This is the basis for all motor applications.
The stator and the rotor are electrical circuits that perform as electromagnets. The stator is the stationary electrical part of the motor. The stator core of a NEMA motor is made up of several hundred thin laminations.
Stator laminations are stacked together forming a hollow cylinder. Coils of insulated wire are inserted into slots of the stator core.
Each grouping of coils, together with the steel core it surrounds, form an electromagnet. Electromagnetism is the principle behind motor operation. The stator windings are connected directly to the power source.
The rotor is the rotating part of the electromagnetic circuit. The most common type of rotor is the "squirrel cage" rotor. Other types of rotor construction will be mentioned later in the course. The construction of the squirrel cage rotor is reminiscent of rotating exercise wheels found in cages of pet rodents.
The rotor consists of a stack of steel laminations with evenly spaced conductor bars around the circumference.
The laminations are stacked together to form a rotor core. Aluminum is die cast in the slots of the rotor core to form a series of conductors around the perimeter of the rotor. Current flow through the conductors form the electromagnet. The conductor bars are mechanically and electrically connected with end rings. The rotor core mounts on a steel shaft to form a rotor assembly.
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