A reluctance-start induction motor is a type of single-phase induction motor designed to achieve self-starting capabilities and improved performance compared to traditional single-phase induction motors. It utilizes a specific design that includes both salient poles and a shading coil to create a rotating magnetic field necessary for motor operation.
Here's how a reluctance-start induction motor works:
Stator: The stator of the motor contains the main winding and an auxiliary winding (shading coil). The main winding is typically wound around the stator poles, while the shading coil is placed on a portion of one of the stator poles.
Rotor: The rotor of the motor is constructed with salient poles, meaning it has distinct protrusions or teeth. These salient poles help in creating variations in reluctance as the rotor rotates within the stator's magnetic field.
Starting Phase: When the motor is initially powered, the alternating current passing through the main winding generates a magnetic field in the stator. At the same time, the shading coil creates a phase difference in the magnetic field on the shaded portion of the stator pole. This phase difference helps in starting the rotation of the rotor in a specific direction.
Reluctance Variation: As the rotor starts to rotate, the salient poles encounter variations in reluctance (resistance to the magnetic field). This causes the rotor to align itself with the stator's rotating magnetic field due to the principle of least reluctance. The rotor tries to minimize the reluctance and aligns itself to achieve this.
Synchronous Speed: The motor accelerates as the rotor follows the rotating magnetic field. Eventually, the rotor reaches a speed close to the synchronous speed determined by the frequency of the power supply and the number of poles in the motor. However, the motor still has a small difference between its rotor speed and the synchronous speed, known as slip.
Running Phase: Once the rotor is in motion, it continues to rotate due to the interaction between the rotating stator magnetic field and the rotor's salient poles. The motor operates as a normal single-phase induction motor at this point.
Reluctance-start induction motors provide better starting torque compared to basic single-phase induction motors, making them suitable for applications where higher starting torque is required. They are commonly used in small appliances, fans, blowers, and other low-power applications. However, they may have limitations in terms of efficiency and performance compared to three-phase induction motors.
It's worth noting that modern motor technology has evolved, and other types of single-phase motors, such as capacitor-start induction motors, capacitor-start capacitor-run induction motors, and permanent split capacitor (PSC) motors, are also widely used today, offering improved efficiency and performance characteristics.