Question

This question is being asked from chapter 5 of the book electric motors and control systems 2nd version and the files attached.

file:///C:/Users/prime/Downloads/ET55a%20Single%20Phase%20AC%20Motors%20%236B.pdf

file:///C:/Users/prime/Downloads/ET55a%20Three%20Phase%20AC%20Motors%20%236A.pdf

1. What are the differences (in construction, starting torque, and operation) between “capacitor start” and “capacitor start/capacitor run” motors?

Answer 1

Different between 'Capacitor start' and 'Capacitor start/capacitor run' motors :

Difference in construction :

In capacitor start motors, only one capacitor (starting capacitor) is used which is in auxiliary winding. Usually electrolytic capacitor is used.

In capacitor start/capacitor run motors, two capacitors (starting capacitor and run capacitor) are used. Starting capacitor is used only at a time of starting whereas run capacitor is connected permanently. Starting capacitor is of electrolytic type and run capacitor is of oil filled type.

Difference in starting torque :

In capacitor start motor, starting torque is higher than capacitor start/capacitor run motor because angle is large in case of capacitor start motor.

But in running condition capacitor start/capacitor run motor gives good torque and power factor.

Difference in operation :

In capacitor start motors, when motor run at sufficient speed then centrifugal switch become open and starting capacitor is disconnected. So this type of motors will give high torque and good power factor at starting but in running condition there is no capacitor to improve torque and power factor.

Now in capacitor start/capacitor run motor, centrifugal switch is connected to starting capacitor. So after starting of motor this switch becomes open and only run capacitor remains connected. Run capacitor gives high torque in running condition as well and it improves power factor. So capacitor start/capacitor run motor is more efficient than capacitor start motor.