Components of three-phase squirrel cage induction motor to determine starting method
Parts of squirrel cage induction motor
Following are the main parts of a squirrel cage induction motor.
- Motor body or frame
- Stator
- Rotor
- Stator winding
- Stator core
- End covers
- Cooling fan
- Bearings
- Dust seals
- Terminal box
- Terminals
- Spacers
- Rotor short-circuiting rings
- Rotor bars
- Motor nameplate
- Stator cooling fins
- Mounting bolts
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| Parts of three-phase squirrel cage induction motor |
Motor body or frame
The motor body or frame is the outer housing encapsulating all motor parts. Motor body or frame is made of cast iron and sometimes it is made of Aluminium to reduce motor weight. Motor body or frame provides housing for stator also.
Stator
The stator is the stationary part of the motor holding motor windings. Motor windings are used to produce a three-phase rotating magnetic field to rotate the station located inside the stator. There is an air gap maintained between the rotor and stator so that rotor can rotate inside the stator minor gape without touching each other.
Rotor
The rotor is the rotating part of the squirrel cage induction motor. The rotor is made of metal sheet laminations bind together to reduce eddy current and hysteresis losses. The rotor is mounted inside the squirrel cage motor with the help of bearings in a way that the rotor can rotate freely inside the minor air gape of the stator. The rotor has bars in it that are short-circuited with the help of short-circuiting rings on both sides. The bars inside the rotor are arranged like a cage which resembles the cage made for squirrels. So that's why the name squirrel cage has been given to such a kind of motor.
Stator windings
Stator windings are a very important part of a squirrel cage induction motor. The windings are used to produce a three-phase rotating magnetic field inside the squirrel cage motor. There are two types of connections for a three-phase motor winding. Star connections and delta connections. The rest there are many types and details about three-phase windings for squirrel cage induction motors. Windings are made of insulated copper wires. Sometimes aluminum wires are also used to reduce weight and cost. Copper windings are places inside slots that are paper insulated. The windings are interconnected on the end of the windings.
Stator core
The stator core is made of silicon steel or an electrical sheet that provides housing for windings and provides a path to magnetic lines of forces or magnetic flux. The stator core has slots to place windings inside. Also, windings are insulated with the help of insulating paper of Myler paper to avoid winding shorting to the ground or motor body.
End covers
Motor end covers are used to pack the motor from the sides. Also motor end cover has bearing housing to center the motor shaft in the middle. Motor end covers also provide arrangements for bearings lubrication and greasing.
Cooling fan or cooling disk
A cooling fan or cooling disk is provided on the free side of the motor which propels air toward the motor body fins to keep the motor cool. Big motors have special arrangements for motor cooling and also motors that run with VFD have a separate motor for cooling the motor. The cooling fan is made of both plastic and sometimes metal.
Bearings
Bearings are mounted on both sides of the squirrel cage induction motor. The shaft is mounted inside the bearings to make sure the uniform air gap between the stator and rotor. Also, bearings provide freedom of rotation to the motor shaft. In big motors, more than two bearings are used. Sometimes there are two bearings on the drive end side and one on the free side or non-drive end side of the motor.
Dust seals
Dust seals are located in both end covers. Dust seals prevent dust entry in the motor and preventing the motor bearings from premature failure. Dust seals also keep the grease inside the bearings and preventing it from leaking. In some poor design motors, dust seals are not provided instead bearings end shield acts like dust seals.
Terminal box
The terminal box encapsulates the motor terminal block. On the terminal block, motor connections are made. The motor terminal box ensures insulated covering on the motor terminals and they are mounted in such a way that the motor terminal box cover can be opened or closed any time to make connections or disconnections with the motor.
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