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Lesson one : learn Motor parts
Motor parts
As the Motor is made up of several parts, this chapter will serve the purpose to show what the parts look like and what they are called. There will also be a brief explanation to what is the purpose of the part that is described.1.1 Outer parts
The stator house holds the stator package and protects the active inner parts from the environment. Another task of the stator house is to help with the heat transfer from inside the motor to the outside, this is the reason why motors often have cooling ribs to increase the surface for better heat dispersion.
The mounting feet and lifting lugs can be found on the stator house. In both ends of the stator house there is the end shields that fixates the bearings holding the shaft and protecting the inside of the motor from the environment.
On top of the motor lies the terminal box that houses the connectors which is used for connecting the motor to the electrical network. It also serves to protect the connectors from water and dust and to protect against live electrical parts.
Coming out of the end shield on one side is the shaft end that transmit torque from the motor to the driven application. The opposite side is referred to as non- drive end or ND end. In the non-drive end we have the fan cover to protect the fan that is mounted on the shaft and also direct the air flow created by the fan over the motor house. At the same time it protects humans, animals and objects from getting in contact with the rotating fan. (McPherson & Laramore, 1990, s. 240)
Figure 1. Outer parts of a motor
1.2Inner parts
The stator core is fixated inside the motor house and is made of laminated electrical steel sheets. The stator core has slots that are filled with copper windings. Its purpose is creating a rotating magnetic field.
The rotor body is the rotating part of the motor and is made of a steel core with aluminium windings. With the use of the rotating magnetic field from the stator, the rotor is able to produce torque.
The rotor body is attached to the shaft in order to transmit the created torque from inside the motor to the driven application.
The rotor and stator together forms the so called active parts of the motor. (McPherson & Laramore, 1990, s. 240-241)
Figure 2. Inner parts of a motor1.3Stator
The stator core consists of several electrically laminated steel sheets which are fixed together to form the stator core. These laminated steel sheets are designed so that when fixated they create slots inside the stator core.
Figure 3. Stator steel sheets
The winding coil is then inserted into the slots of the stator core. Some might wonder why use laminated sheets instead of just one big iron core. The reason is to reduce the induced current in the stator which leads to overheating of the motor and energy losses that could be used for creating the magnetic field instead. This unwanted induced current is also called eddy current.
Figure 4. Stator1.4Rotor
The rotor is the rotating part of the motor and can be found inside the stator. As with the stator, also the rotor core consists of electrically laminated steel sheets. Inside the rotor slots there are aluminium windings that are casted together with short-circuit rings.
This is done by making holes in the lamination so that when they are stacked, channels will be formed through the rotor core. During the casting these channels will fill up with aluminium and form the windings that together with the short-circuit rings are shaped like a squirrel cage. Hence the name squirrel cage induction motor.
The windings inside the rotor do not go straight but are skewered for the purpose of reducing electrical noise and vibration. The rotor core helps conducting the magnetic field from the stator to the rotor windings.
There is an air gap between the stator and the rotor and since it is known that air conducts magnetic fields poorly the gap can’t to be too big. The airgap cannot either be too small since metallic objects expand when heated and as the rotor gets warm there will not be enough space for it to rotate inside the stator. The rotor windings can also be called for rotor bars.
Next up is explaining how the rotor is able to spin inside the stator but first electromagnetic induction has to be explained.
Figure 5. Squirrel cage rotor
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