The centrifugal switch is an essential component in many single-phase induction motors. Its primary role is to disconnect the starting winding from the motor circuit once the motor reaches a certain speed. This switch is usually installed in motors that require an auxiliary winding to start rotating.
Here's how it works:
Starting phase: When the single-phase induction motor is initially switched on, it needs some mechanism to generate a rotating magnetic field to start rotating. To achieve this, the motor has two windings - the main running winding and the starting winding (also known as the auxiliary winding). The starting winding is positioned at an angle to the main winding, creating a phase difference between the two windings, which generates the initial rotating magnetic field.
Role of the centrifugal switch: The centrifugal switch is a mechanical device typically mounted on the motor's shaft. As the motor starts rotating, the centrifugal force comes into play. The centrifugal switch is designed to be held closed during the starting phase when the motor is at rest or spinning at low speeds. This keeps the starting winding connected in the circuit.
Switching off the starting winding: Once the motor reaches a certain speed (usually around 70-80% of its synchronous speed), the centrifugal force overcomes the spring tension in the switch, causing it to open or disconnect the starting winding from the circuit. At this point, the motor continues to run using only the main running winding, which is designed for continuous operation.
Why disconnect the starting winding: The starting winding is designed with fewer turns of thicker wire to provide high starting torque but is not suitable for continuous operation. Leaving the starting winding connected during normal running would result in inefficient operation, excessive heating, and potential damage to the winding due to its higher resistance and reactance compared to the main running winding.
By disconnecting the starting winding at the appropriate speed, the centrifugal switch ensures that the motor operates efficiently with reduced losses and prevents overheating of the starting winding. This mechanism allows single-phase induction motors to start reliably and transition smoothly into their running mode, making them suitable for various applications in household appliances, small pumps, fans, and other low-power applications.