Capacitor Start Induction Motor
Table of Contents
Capacitor Start Induction Motor
Capacitor Start Induction Motor
In order to create a greater phase difference between the current in the main and Auxiliary Windings, capacitor start induction motor, which are Single-phase induction motors, use a Capacitor in the Auxiliary winding circuit. The fact that the name “Capacitor starts itself” implies that the motor uses a Capacitor to start itself is clear. A Capacitor Start Induction Motor’s connection diagram is shown in the figure below.
The cage rotor and two windings on the stator of the capacitor start motor are both present. They are referred to as the starting winding and the auxiliary winding, respectively. So One winding is 90 degrees away from the other. The starting winding is connected in series with a Capacitor designated as CS. The circuit is also wired up with a Centrifugal switch, model SC.
The Phasor Diagram of the Capacitor Start Induction Motor is shown below:
According to the phasor diagram above, IM, the current in the main winding, is 90 degrees lagging IA, the current in the auxiliary winding. A single-phase supply current is divided into two phases as a result. The MMFs of the two windings are equal in magnitude but offset by 90 degrees in the time phase, and they are electrically 90 degrees apart. As a balanced two-phase motor, the motor operates. So The centrifugal switch installed on the motor shaft automatically disconnects the auxiliary winding and the starting capacitor as the motor approaches its rated speed.
Characteristics of the Capacitor Start Motor
The starting torque of the Capacitor Start Induction Motor is about three to four times greater than the full load torque. The two conditions are necessary in order to get a high starting torque. These are what they are:-
- The Starting capacitor value must be large.
- The valve of the starting winding resistance must be low.
The electrolytic capacitors of the order of the 250 µF are used because of the high Var rating of the capacitor requirement.
The Torque Speed Characteristic of the motor is shown below:
The characteristic shows that the starting torque is high. The cost of this motor is more as compared to the split-phase motor because of the additional cost of the capacitor. The Capacitor start motor can be reversed by first bringing the motor to rest condition and then reversing the connections of one of the windings.
Applications of Capacitor Start Induction Motor
The various applications of the motor are as follows:
- Used in pumps and compressors
- These motors are utilised for heavier loads that require frequent starts.
- They are also used for conveyors and machine tools
- Used in the refrigerator and air conditioner compressors.