Permanent capacitor run motor 4. Capacitor start capacitor run motor 5.
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Shaded pole motor The rotating magnetic field is produced when there are minimum two alternating fluxes, having a phase difference between them. The resultant of these two fluxes produces a rotating flux which rotates in space in one particular direction. So in all the above methods or say types of induction motors, the additional flux other than main flux should have a certain phase difference with respect to main or stator flux.
If the phase difference is more, starting torque will be more. So the starting torque of the motor depends on the rotating magnetic field and thereby, additional means whether it is an auxiliary winding or anything.
Principle of Operation - Johnson Electric, Application of shaded pole single phase induction motor
Once the motor picks up the speed, this additional winding is removed from the supply. This is the basic principle followed by all these types of single phase induction motors.
Let us discuss these types of motors in brief. Split Phase Induction Motor This is one of the most widely used types of single phase induction motors. The essential parts of the split phase motor include main winding, auxiliary winding and a centrifugal switch. This is the simplest arrangement to set up a rotating magnetic field by providing two winding on the same stator core as shown in figure.
The auxiliary or starting winding carries a series resistance such that its impedance becomes highly resistive in nature.
Application of shaded pole single phase induction motor
It is not wound identical to the main winding but contains fewer turns of much smaller diameter as compared to main winding. This will reduce the amount of start current lags the voltage. The main winding is inductive in nature in such that current lags the voltage by some angle. These two windings are connected in parallel across the supply.
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Due to the inductive nature, current through main winding lags the supply voltage by a large angle while the current through starting winding is almost in phase with voltage due to resistive nature. Hence there exists a phase difference between these currents and thereby phase difference between the fluxes produced by these currents. The resultant of these two fluxes produce rotating magnetic field and hence the starting torque. The centrifugal switch is connected in series with the starting winding.
When the motor reaches 75 to 80 percent of synchronous speed, the centrifugal switch is opened mechanically and thereby mann sucht frau mit bild winding is out of the circuit. Therefore, the motor runs only with main winding. Split phase motors give poor starting torque due to small phase difference between main and auxiliary currents.
Also, the power factor of these motors is poor. These are mainly used for easily started loads such as blowers, fans, washing machines, grinders, etc. Capacitor Start Induction Motor This motor is similar to the split phase motor, but in addition a capacitor is connected in series to auxiliary winding.
This is a modified application of shaded pole single phase induction motor of split phase motor. Since the capacitor draws a leading current, the use of a capacitor increases the phase angle between the two currents main and auxiliary and hence the starting torque.
This is the main reason for using a capacitor in single phase induction motors.
Here the capacitor is of dry-type electrolytic one which is designed only for alternating current use. Due to the inexpensive type of capacitors, these motors become more popular in wide applications.
These capacitors are designed for definite duty cycle, but not for continuous use. The schematic diagram of application of shaded pole single phase induction motor start motor is shown in figure below.
Types of Single Phase Induction Motors
Once the speed is picked up, the additional winding along with capacitor is removed from the circuit with the help of centrifugal switch. But, the difference is that the torque produced by this motor is higher than split phase motor due to the use of capacitor. Due to the presence of a capacitor, the current through auxiliary winding will leads the applied voltage by some angle which is more than that of split case type.
Thus, the phase difference between main and auxiliary currents is increased and thereby starting torque. The performance of this motor is identical to the split phase motor when it runs near full load RPM. Due to the capacitor, the inrush currents are reduced in this motor. However the power factor is low at rated load and rated speed.