Introduction
Capacitor start capacitor run induction motor is a type of single-phase induction motor that uses two capacitors for improved starting and running performance. It combines the benefits of both capacitor start and capacitor run motors, making it suitable for applications requiring high starting torque and efficient running performance.
Construction of Capacitor Start Capacitor Run Motor
This motor consists of the following major parts:
- Stator: Contains two windings – main winding and auxiliary winding.
- Rotor: Usually a squirrel cage rotor is used.
- Start Capacitor (Cs): Connected in series with the auxiliary winding during startup for high starting torque.
- Run Capacitor (Cr): Remains permanently connected in the circuit for efficient running.
- Centrifugal Switch: Disconnects the start capacitor from the circuit once the motor reaches ~75% of synchronous speed.
Working Principle
At the time of starting, both the start capacitor and run capacitor are connected in parallel to the auxiliary winding, creating a phase shift and generating a rotating magnetic field which initiates rotation. Once the motor reaches about 75% of its rated speed, the centrifugal switch opens and disconnects the start capacitor, leaving the run capacitor in the circuit for smooth and efficient running.
Advantages
- High starting torque
- Better efficiency during running condition
- Improved power factor
- Smoother operation
- Suitable for high-load starting applications
Disadvantages
- More expensive than single capacitor motors
- Requires centrifugal switch (extra component)
- More complex wiring
Applications
- Air compressors
- Refrigerators
- Air conditioners
- Conveyors
- Pumps and blowers
Comparison with Other Single-Phase Motors
|
Feature |
Capacitor Start
Motor |
Capacitor Run
Motor |
|
Starting Torque |
High |
Low |
|
Running Efficiency |
Moderate |
Good |
|
Capacitor in
Running |
No |
Yes |
|
Complexity |
Low |
Low |
FAQs
Q1. Why are two capacitors used in a capacitor start capacitor run motor?
Ans: One capacitor (start capacitor) provides high starting torque and is disconnected after startup. The other (run capacitor) remains in the circuit for better efficiency and smoother running.
Q2. What is the role of the centrifugal switch in this motor?
Ans: The centrifugal switch disconnects the start capacitor from the circuit once the motor reaches around 75% of its speed.
Q3. Can we use this motor for heavy load starting?
Ans: Yes, due to its high starting torque, it is suitable for applications like compressors and pumps.
Q4. What type of rotor is used in this motor?
Ans: It typically uses a squirrel cage rotor.
Q5. How is it different from a split-phase induction motor?
Ans: A split-phase motor doesn't use capacitors and has low starting torque, whereas this motor uses capacitors to improve performance.
Conclusion
Capacitor start capacitor run induction motors are ideal for applications requiring both high starting torque and smooth running operation. Though they are costlier than other single-phase motors, their performance and efficiency make them a preferred choice in many industrial and commercial setups.