To understand how the starting winding of a single-phase motor works, it's important to recognize its role in getting the motor up to speed. Single-phase motors require a starting mechanism to produce a rotating magnetic field. This is typically achieved via an additional starting winding.

Once the motor reaches a certain speed, it is necessary to disconnect the starting winding to prevent power loss and possible damage. There are several methods to achieve this:

• Magnetic Relay: A magnetic relay is an electrically operated switch that uses an electromagnetic coil to open or close contacts in circuits. It disconnects the starting winding when the rated speed is reached, ensuring efficiency and protecting the motor.
• Thermal Relay: This type involves a bimetallic strip that activates by heat. It’s generally used for overload protection rather than controlling start windings.
• Centrifugal Switch: A mechanical device that uses centrifugal force to switch the circuit as the motor speed increases. It's common in some motor setups, but not typically in modern refrigerators.

For refrigerators, which often use capacitor start motors, the starting winding is usually disconnected by a magnetic relay due to its reliability and suitability for the electrical demands.

Therefore, the correct answer is: magnetic relay.