A centrifugal switch is a mechanical device used in single-phase induction motors to assist in switching off the starting winding once the motor reaches a certain speed. Single-phase induction motors use two windings for their operation: the main running winding and the starting winding. The starting winding provides the initial torque required to start the motor, but it is not designed to run continuously. If the starting winding remains energized while the motor is running at full speed, it can cause inefficiencies and overheat the motor.
The centrifugal switch is typically mounted on the motor shaft, close to the motor's rotor or flywheel. It consists of two main components: stationary contacts and rotating weights. Here's how the centrifugal switch works to switch off the starting winding:
Starting Phase: When the motor is initially switched on, both the main running winding and the starting winding are energized. The motor starts to rotate from rest, and the centrifugal switch is also stationary at this point.
Centrifugal Force: As the motor accelerates, the motor's rotor and the attached centrifugal switch weights start to spin. The centrifugal force generated by the spinning weights causes them to move outward along the shaft.
Switch Transition: As the weights move outward, they are connected to the stationary contacts of the switch through mechanical linkages. When the weights reach a certain speed (usually just before the motor reaches its normal operating speed), the centrifugal force becomes strong enough to overcome the spring tension that holds the switch closed.
Switch Opening: Once the switch opens due to the centrifugal force, it interrupts the circuit to the starting winding, effectively disconnecting it from the power supply. The motor continues to run using only the main running winding, which is designed for continuous operation at higher speeds.
Running Phase: With the starting winding disconnected, the motor operates efficiently using only the main running winding. The centrifugal switch remains in the open position as long as the motor is running.
The centrifugal switch's operation relies on the principles of centrifugal force and mechanical linkage. It's a simple yet effective method to ensure that the starting winding is only active during the startup phase when it's needed most. Once the motor reaches its desired speed, the switch disconnects the starting winding to prevent overheating and excessive energy consumption.