Function of Starting Relay, Capacitors and OLP (Over Load Protector)

In refrigeration and air conditioning systems, especially in single-phase compressor motors, several electrical accessories are used to ensure safe starting, smooth operation, and protection of the motor. Among these, starting relay, capacitors, and OLP (Over Load Protector) play a very important role. In the ITI RAC trade, understanding their functions is essential for installation, servicing, and troubleshooting.

1. Starting Relay

Function

A starting relay is used to connect and disconnect the starting winding of the motor during starting. It ensures that the starting winding is energized only for a short duration to provide starting torque.

Working

• When the motor is switched ON, the relay connects the starting winding to the circuit.
• The motor starts and gains speed.
• Once the motor reaches about 70–80% of its rated speed, the relay disconnects the starting winding.

Types of Starting Relays

• Current relay
• Potential relay
• PTC (Positive Temperature Coefficient) relay

Importance

• Provides proper starting of motor
• Prevents overheating of starting winding
• Improves motor efficiency

2. Capacitors

Function

Capacitors are used to create a phase difference between the current in the starting and running windings. This phase difference helps in producing a rotating magnetic field and increases starting torque.

Types of Capacitors

a) Starting Capacitor

• Used only during starting
• Provides high starting torque
• Disconnected after motor starts

b) Running Capacitor

• Remains in the circuit during operation
• Improves efficiency and power factor

c) Combined (Start-Run) Capacitor

• Used in CSR motors
• Provides both starting and running functions

Importance

• Improves starting performance
• Reduces current consumption
• Ensures smooth operation

3. OLP (Over Load Protector)

Function

The Over Load Protector (OLP) is a safety device used to protect the motor and compressor from damage due to overload, overheating, or excessive current.

Working

• When current exceeds the safe limit or temperature rises, the OLP disconnects the power supply.
• After cooling down, it automatically resets and restores the circuit.

Types of OLP

• Thermal overload protector
• Current overload protector

Importance

• Prevents motor burning
• Protects against overcurrent and overheating
• Increases life of compressor

Applications in Refrigeration Systems

• Refrigerator compressors
• Air conditioners
• Water coolers
• Deep freezers

Conclusion

Starting relay, capacitors, and OLP are essential components in single-phase motors used in refrigeration and air conditioning systems. Each component has a specific function that ensures proper starting, efficient operation, and protection of the motor.

A clear understanding of these devices helps RAC students and technicians in diagnosing faults, performing maintenance, and ensuring safe operation of electrical equipment.