Construction of Single-Phase Induction Motors
The single-phase induction mac hine is the most frequently used motor for refrigerators, washing machines, clocks, drills, compresssors, pumps, and so forth.
The constructional details of sin gle phase induction motor are shown in figure 3. 8.
The single-phase motor stator has a laminated iron core with two windings arranged perpendicularly. One is the main and other is the auxiliary winding or starting winding.
The rotor of single phase induction motor is shown in figure 3.9. The co nstruction of the rotor of the single phase induction motor is similar to the squirrel cage three phase inductions motor. The r otor is cylindrical in shape and has slots all o ver its periphery. The slots are not made parallel to each other but are bit skewed as the skewing prevents magnetic locking of stator and rotor teeth and makes the working of induction motor more smooth and quieter. The squirrel cage rotor consists of aluminium, brass or copper bars. These aluminiumo r copper bars are called rotor conductors and are placed in the slots on the periphery of the rotor. The rotor conductors are permanent ly shorted by the copper or aluminiumrings called the end rings. In order to provide mechanical strength these rotor conductor are braced to the end ring and hence form a complete closed circuit resembling like a cage annd hence got its name as "squirrel cage inductio n motor". As the bars are permanently shorted by end rings, the rotor electrical resistance is very small and it is not possible to add external resistance as the bars are permanently shorted. The absence of slip ring and brushes make the construction of single phase induction motor very simple and robust.
When single phase ac supply is given to the stator winding of single phase induction motor, the alternating current starts flowing through the stator or main winding. This alternating current produces an alternating flux called main flux. This main flux also links with the rotor conductors and hence cut the rotor conductors. According to the Faraday’s law of electromagnetic induction, emf gets induced in the rotor. As the rotor circuit is closed one so, the current starts flowing in the rotor. This current is called the rotor current. This rotor current produces its own flux called rotor flux. Since this flux is produced due to induction principle so, the motor working on this principle got its name as induction motor. Now there are two fluxes one is main flux and another is called rotor flux. These two fluxes produce the desired torque which is required by the motor to rotate.