1 phase induction motor

it is all about 1 phase induction motor

1. G.H.PATEL COLLEGE OF ENGINNERING AND TECHNOLOGY NAME: KOTHADIA YASH – 150110109019 LALKIYA ABHISHEK -150110109020 Guided by jignesh payel & jasmin james

2. 1-¢ induction motor

3. Introduction Construction of a single phase induction motor is similar to the  construction of three phase induction motor  having squirrel cage rotor, except that the stator is wound for single phase supply. Stator is also provided with a 'starting winding' which is used only for starting purpose. This can be understood from the  schematic of single phase induction motor  at the left.

4. Working Principle Of Single Phase Induction Motor When the stator of a single phase motor is fed with single phase supply, it produces alternating flux in the stator winding.  The alternating current flowing through stator winding causes induced current in the rotor bars (of the  squirrel cage rotor  ) according to  Faraday's law of electromagnetic induction . This induced current in the rotor will also produce alternating flux. Even after both alternating fluxes are set up, the motor fails to start (the reason is explained below). However, if the rotor is given a initial start by external force in either direction, then motor accelerates to its final speed and keeps running with its rated speed. This behavior of a single phase motor can be explained by double-field revolving theory.

5. Double-Field Revolving Theory The double-field revolving theory states that, any alternating quantity (here, alternating flux) can be resolved into two components having magnitude half of the maximum magnitude of the alternating quantity, and both these components rotating in opposite direction. Following figures will help you understanding the double field revolving theory.

6. Why Single Phase Induction Motor Is Not Self Starting? The stator of a single phase induction motor is wound with single phase winding. When the stator is fed with a single phase supply, it produces alternating flux (which alternates along one space axis only). Alternating flux acting on a squirrel cage rotor can not produce rotation, only  revolving flux  can. That is why a single phase induction motor is not self starting.

7. How To Make Single Phase Induction Motor Self Starting ? As explained above,  single phase induction motor is not self-starting . To make it self-starting, it can be temporarily converted into a two-phase motor while starting. This can be achieved by introducing an additional 'starting winding' also called as auxillary winding. Hence, stator of a single phase motor has two windings: ( i ) Main winding and (ii) Starting winding ( auxillary winding). These two windings are connected in parallel across a single phase supply and are spaced 90 electrical degrees apart. Phase difference of 90 degree can be achieved by connecting a capacitor in series with the starting winding. 

8. Hence the motor behaves like a two-phase motor and the stator produces revolving magnetic field which causes rotor to run. Once motor gathers speed, say up to 80 or 90% of its normal speed, the starting winding gets disconnected form the circuit by means of a centrifugal switch, and the motor runs only on main winding.

9. Methods for Making Single Phase Induction as Self Starting Motor Split phase induction motor, Capacitor start  inductor  motor, Capacitor start  capacitor  run induction motor, Shaded pole induction motor. Permanent split capacitor motor or single value capacitor motor.

10. Split Phase Induction Motor In addition to the main winding or running winding, the stator of single phase induction motor carries another winding called auxiliary winding or starting winding. A centrifugal switch is connected in series with auxiliary winding. The purpose of this switch is to disconnect the auxiliary winding from the main circuit when the motor attains a speed up to 75 to 80% of the synchronous speed. We know that the running winding is inductive in nature. Our aim is to create the phase difference between the two winding and this is possible if the starting winding carries high  resistance . Let us say I run  is the  current  flowing through the main or running winding, I start  is the current flowing in starting winding, and V T is the supply voltage.

11.  In  split phase induction motor  the starting and main current get spitted from each other by some angle so this motor got its name as split phase induction motor.

12. Capacitor Start IM and Capacitor Start Capacitor Run IM

13. The working principle and construction of Capacitor start  inductor  motors and capacitor start capacitor run induction motors are almost the same. We already know that single phase induction motor is not self starting because the magnetic field produced is not rotating type. In order to produce rotating magnetic field there must be some phase difference.

14. In case of split phase  induction motor  we use resistance for creating phase difference but here we use capacitor for this purpose.So , in  capacitor start inductor motor  and  capacitor start capacitor run induction motor  we are using two winding, the main winding and the starting winding. With starting winding we connect a capacitor so the current flowing in the capacitor i.e I st  leads the applied voltage by some angle, φ st .

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