The centrifugal switch is a component used in some single-phase induction motors to facilitate their starting process. Single-phase induction motors inherently lack a rotating magnetic field, which makes them difficult to start on their own. The centrifugal switch mechanism helps overcome this limitation and assists in the motor's initial startup.
Here's how the concept of the centrifugal switch starting works:
Starting Winding: Single-phase induction motors typically have two windings: the main winding and the starting winding. The main winding is responsible for producing the main magnetic field required for the motor's operation, while the starting winding produces an auxiliary magnetic field to initiate rotation during startup.
Centrifugal Switch: The centrifugal switch is a mechanical switch that is usually located on the motor's shaft, near the rotor. It consists of two contacts that are normally closed when the motor is at rest (not running). The switch is operated by centrifugal force, which is generated as the motor's rotor starts to spin.
Startup Process: When the motor is initially powered, both the main winding and the starting winding are energized. The starting winding creates a second magnetic field that is slightly out of phase with the main winding's magnetic field. This phase difference results in a rotating magnetic field, which induces a starting torque on the rotor.
Centrifugal Force Activation: As the rotor begins to spin, the centrifugal force increases. At a certain speed, the centrifugal force becomes sufficient to overcome the spring tension or other mechanism holding the centrifugal switch's contacts closed.
Switch Transition: Once the centrifugal force reaches the required threshold, it forces the contacts of the centrifugal switch to open. This action disconnects the starting winding from the circuit. Since the starting winding's magnetic field was used primarily for the startup phase, its disconnection does not significantly affect the motor's operation.
Steady State Operation: With the starting winding disconnected, the motor relies solely on the main winding to create a rotating magnetic field. The motor then operates as a typical single-phase induction motor, generating a continuous torque and maintaining its rotation.
In summary, the centrifugal switch is a mechanism used in single-phase induction motors to disconnect the starting winding once the motor reaches a sufficient speed. This helps in providing the initial push required for the motor to overcome its static inertia and start rotating. Once the motor is up to speed, it operates using the main winding to maintain its rotation.