- Split phase induction motor consists of two winds one is main winding and another is auxiliary winding.
- The main winding has low resistance and high reactance while starting winding has high resistance and low reactance.
- The resistance of starting winding can be increased or decreased by connecting a resistance series with starting winding, the value of this resistance is generally high and made up of fine copper.
- The starting winding current (Is) lag behind applied voltage V by a small angle while the main winding current (Im) lags behind applied voltage V by a very large angle.
- The phase angle between starting winding current (Is) and the main winding current (Im) is made as large as possible because of starting torque of the split phase induction motor is directly proportional to the sin angle between Is and Im.
Starting torque(Tst) = K. Sin(angle between Im and Is)
- A centrifugal switch (C.S) is connected in series with the start of winding as shown in the diagram and its function is to disconnect automatically when the motor achieved 70% to 80% of its full load speed.
- Centrifugal switch is used often motor rating is about 100W or above and for a small motor, the relay is used.
- A typical torque-speed characteristic of the split-phase induction motor is shown below.
- From the characteristics, it is observed that the starting torque of the motor is 150% to 200% of full load torque and therefore starting current is 6 to 8 times of full load current.
The direction of rotation of the split-phase induction motor can be reversed by reversing the line connection of either winding.
Application:
- This motor is often used in preference to a costlier capacitor-type motor.
- Typically an application is a Fan, Blower, Centrifugal pump, Washing machine, Small machine tools, oil burner, etc.
- Commonly available size is 0.05HP to 0.3HP or 40KW to 250KW with speed range from 865 RPM to 3450 RPM.