Induction motors are the most common type of three phase (3~) electric motor employed today. They are relatively cheap, easy to maintain, very robust and come in a range of sizes. These types of motors are employed throughout the world in many industries.
Induction motors are often referred to as squirrel cage motors due to the design of the motor rotor. The name ‘induction’ refers to the fact that an electrical current is induced in the rotor cage when the motor is in operation; this differs to other motors where the rotor current is supplied externally.
This 3D model shows all major components associated with a typical electrical induction motor, these include:
- Fan Casing
- Dust Guard/Seal
- Shaft Key
- Motor Housing
- Motor End Casing
- Terminal/Connection Block
- Retaining Rings
A cover prevents accidental damage occurring to the fan and personnel.
A fan is used to force cool the motor. Air is drawn through the fan cover grills due to the negative pressure created by the fan, the air is then directed across the motor housing. Flowing air cools the motor and reduces the risk of overheating.
Nuts and bolts are used for securing parts of the motor together. Chosen nuts should have suitable tensile strength and corrosion resistance characteristics.
Nuts are the ‘female’ part of a nut and bolt assembly.
Locking washers are used to apply a continual tensile (stretching force) to the bolt and nut assembly. The tensile force reduces the possibility of the nut loosening due to vibration.
The plain washer distributes the compressor force exerted by the nut and bolt assembly when tightened. The washer also prevents the nut and bolt from ‘digging’ into the metal surfaces when being tightened.
Motor End Cover
The end cover houses the bearing, c-clip and sometimes a dust seal. The two end covers support the weight of the shaft.
The bearing is housed in this space.
The c-clip is installed with c-clip pliers. After opening the pliers, the c-clip expands due to residual tensile forces. The residual force keeps the c-clip firmly within the groove and prevents axial movement of the bearing.
Sealed Ball Bearing
A sealed ball bearing allows the rotor to rotate without transferring the rotary motion to other stationary parts i.e. the motor housing.
C-Clip / Retaining Ring
A retaining ring is used to retain the bearing within the motor end cover housing. The ring prevents axial movement of the bearing.
Nuts and bolts are used for securing parts of the motor together. Chosen bolts should have suitable tensile strength and corrosion resistance characteristics.
Bolts are the ‘male’ part of a nut and bolt assembly.
Motor Casing / Housing
The motor casing houses the stator and rotor assembly. The casing must be strong enough to withstand the electrical and mechanical stresses generated by the motor as well as the physical demands of its working environment e.g. severe weather.
The stator contains the insulated windings for the three phases of the motor.
The electrical current flowing through these windings is what causes the rotor to rotate.
The stator core is usually constructed of iron to reduce load losses.
Radiator fins increase the motor casing surface area. A larger surface area allows heat to be removed more quickly by the forced air flow from the fan.
The three phase supply and earth cable are connected to the terminal board. Each of the three phases of the motor must be correctly wired to the incoming supply. Motors are connected in either a star or delta wiring configuration.
The terminal housing shields the connection board and electrical connections from foreign object damage such as water.
The lifting eye allows moving of the motor using a strop, rope, crane, chain block or cable etc. It is a requirement if the motor is too large to be moved using only manual labour. Multiple lifting eyes may be used for large motors.
Usually constructed of rubber or card. The gasket is ‘squeezed’ between the two metal surfaces in order to create a sealed space. The gasket prevents water or contamination from passing between the metal surfaces and into the terminal casing.
Feet / Base
The complete weight of the motor is transferred to the structure or ground through the feet. The base has holes or channels drilled into it to allow alignment and fixture of the motor.
The rotor shaft connects the rotor to the bearings, fan and load. When installing, the rotor is sometimes cooled and the bearings heated in order to allow easy assembly (only for small motors).
The rotor core is constructed of steel laminations. The magnetic field created by the stator windings acts upon the rotor and causes it to turn. The type of rotor used in this example is a cage rotor (squirrel cage motor).
Click here to see a 3D rotor.
The shaft key is the only connection between the rotor shaft and the load being driven, it is thus imperative the key can withstand the full load characteristics of the motor without failing.
The end ring is used to compress the steel laminations together.
Shaft Key Groove
The shaft key sits within this groove.
Depending upon the design, a rubber dust seal may sit in this space. The seal reduces the risk of contamination entering the motor housing. The seal is pressed between the rotor shaft and motor end cover.