It has got the same construction features as the DC motor, which is composed of two basic parts: rotating part called rotor and stationary part named stator.
And the stator is composed of stampings, which were slotted on its periphery to support two windings named the stator winding and main winding. A single phase ac supply would excite the laminated component and make it keep iron losses at a minimum amount. The stampings are composed of material like silicon steel which minimises the hysteresis loss. When excited by single phase AC supply, the stator winding is wound for certain definite number of poles means. Stator builds the magnetic field which generates the effect of certain definite number of poles. The number of poles for which stator winding is wound, decides the synchronous speed of the motor. The synchronous speed is denoted as “Ns” and it has a fixed relation with supply frequency “f” and number of poles “P”. The relation is shown as,
The induction motor often rotates slightly lower than the synchronous speed, rather than runs at a same speed with the synchronous.
The rotor construction could be said as squirrel cage type. For this one, rotor includes uninsulated copper or aluminium bars and is placed in the slots. With the hand of conducting rings, also named end rings, the bars are permanently shorted at both the ends. It is named as squirrel cage rotor for its whole structure has got a feature as cage. The construction and symbol is shown in the Fig.1
The entire rotor’s resistance is rather slight, because the bars are permanently shorted to each other. And the air gap between stator and rotor is kept uniform and as small as possible. As that of the stator winding, the basic feature of this rotor is that it automatically adjusts itself for same number of poles.
The schematic representation of two pole single phase induction motor is shown in the Fig.2.