Study of Shaded Pole Motor, RSIR, CSIR, CSR and PSC Motors
In the ITI Refrigeration and Air Conditioning (RAC) trade, different types of single-phase induction motors are used depending on the requirement of starting torque, efficiency, and application. This chapter explains the construction and working of shaded pole motor, RSIR, CSIR, CSR, and PSC motors, which are commonly used in refrigeration and air conditioning systems.
1. Shaded Pole Motor
Construction
- Stator with salient poles
- Shading coil (copper ring) on a portion of each pole
- Squirrel cage rotor
Working
When AC supply is applied, current flows through the stator winding and produces a magnetic field. The shading coil delays the magnetic flux in part of the pole, creating a weak rotating magnetic field. This causes the rotor to rotate from the unshaded part to the shaded part of the pole.
Characteristics
- Very low starting torque
- Simple and low-cost construction
- Low efficiency
Applications
- Small fans
- Exhaust fans
- Blowers
2. RSIR Motor (Resistance Start Induction Run)
Construction
- Main (running) winding
- Starting winding with high resistance
- Centrifugal switch
Working
The high resistance of the starting winding creates a phase difference between currents in the two windings, producing starting torque. After the motor reaches about 70–80% speed, the centrifugal switch disconnects the starting winding.
Characteristics
- Moderate starting torque
- Simple design
Applications
- Small compressors
- Pumps
3. CSIR Motor (Capacitor Start Induction Run)
Construction
- Main winding
- Starting winding with capacitor
- Centrifugal switch
Working
A capacitor is connected in series with the starting winding to create a large phase difference, resulting in high starting torque. The starting winding is disconnected after the motor reaches a certain speed.
Characteristics
- High starting torque
- Improved efficiency
Applications
- Refrigerator compressors
- Air conditioners
4. CSR Motor (Capacitor Start Capacitor Run)
Construction
- Main winding
- Auxiliary winding
- Two capacitors (start capacitor and run capacitor)
- Centrifugal switch
Working
During starting, both capacitors are connected to provide very high starting torque. After the motor reaches operating speed, the start capacitor is disconnected, and the run capacitor remains in the circuit for efficient operation.
Characteristics
- Very high starting torque
- High efficiency and power factor
Applications
- Air conditioners
- Heavy-duty compressors
5. PSC Motor (Permanent Split Capacitor Motor)
Construction
- Main winding
- Auxiliary winding
- Single capacitor (always connected)
Working
The capacitor is permanently connected in series with the auxiliary winding. It provides a phase difference for both starting and running. These motors do not use a centrifugal switch.
Characteristics
- Moderate starting torque
- Smooth and quiet operation
- High efficiency
Applications
- Fans and blowers
- Evaporator and condenser motors
Comparison of Motors
| Motor Type | Starting Torque | Efficiency | Application |
|---|---|---|---|
| Shaded Pole | Very Low | Low | Small fans |
| RSIR | Moderate | Moderate | Small compressors |
| CSIR | High | Good | Refrigerators |
| CSR | Very High | High | Air conditioners |
| PSC | Moderate | High | Fans and blowers |
Conclusion
Different types of single-phase motors are used based on the requirement of starting torque and efficiency. Shaded pole motors are simple but have low torque, while capacitor-based motors such as CSIR and CSR provide high starting torque and efficiency.
Understanding these motors helps RAC students in selecting, installing, and maintaining electrical components used in refrigeration and air conditioning systems.