Asynchronous Motor

Induction motors are alternating current motors widely used in industry, consisting of two main parts called the stator and rotor, and they do not operate at a fixed speed. They are low-cost and require minimal maintenance. The most commonly used motor type today, Induction Motors, are manufactured in single-phase and three-phase configurations. Due to their durability, low cost and high efficiency, induction motors are extensively used in industrial applications such as conveying systems, fans, pumps, reducers and compressors. Because induction motors are employed across a wide range of industrial applications, they account for a significant portion of global energy consumption. Therefore, motor efficiency plays a critical role in global energy conservation. The efficiency of induction motors has been significantly improved across a broad spectrum through advances in design, maintenance, repair and control methods. In general, the efficiency of induction motors varies depending on the application and operating conditions. Therefore, proper sizing and operation of motors are crucial to achieving maximum efficiency.

The most important feature distinguishing induction motors from synchronous motors is that their rotational speed is not fixed. Induction machines are also referred to as induction machines in terms of operating principle. Due to their low cost and absence of brushes and commutators, they experience fewer faults and require less maintenance. For this reason, they are widely used in industry. The production of induction motors is cheaper than that of direct current machines, but their control is more complex. An induction motor consists of two main parts: the stator and the rotor. The stationary part is called the stator, while the rotating part is called the rotor. The function of the stator is to generate a magnetic field, while the function of the rotor is to produce the force that drives motion. The rotor is supported by bearings housed in end caps mounted on both sides of the stator and rotates freely with an appropriate air gap.

^{3 Fazlı Asenkron Motor - (}Gamak⁾

The stator is the stationary part of the induction motor. It consists of windings and a laminated core. The laminated core is formed by stacking special insulated sheets with a thickness of 0.4 to 0.8 mm. The stator windings are obtained by winding copper wire around the core for a specific number of turns. The structure of the winding determines the number of poles in the motor.

The rotor is the rotating part of an induction motor. Induction motors are classified into two types based on rotor construction: squirrel-cage induction motors and wound-rotor induction motors. The rotor of a squirrel-cage induction motor consists of a series of conductive bars placed in slots on the rotor surface and short-circuited at both ends by large end rings. This design is called a squirrel-cage. The other rotor type is the wound-rotor induction motor. A wound rotor has a complete three-phase winding set similar to the stator winding. The three phases of the rotor winding are typically connected in a Y (star) configuration, and the ends of the three rotor conductors are connected to slip rings mounted on the rotor shaft. The rotor windings are short-circuited via brushes that slide on the slip rings. As a result, additional resistance can be added to the rotor circuit of wound-rotor induction motors. This allows the rotor current to be adjusted. Furthermore, this feature can be utilized to modify the torque-speed characteristic of the motor.

Wound-rotor induction motors are more expensive than squirrel-cage motors. In addition, due to wear associated with brushes and slip rings, they require significantly more maintenance. For this reason, wound-rotor motors are less preferred in industry compared to squirrel-cage motors.

When an AC voltage is applied to the stator of an induction motor, alternating current flows through the stator windings. This alternating current generates a rotating magnetic field in the magnetic circuit. This alternating field can be expressed as a Fourier series. Each harmonic of the alternating field can be separated into two rotating fields rotating at the same angular velocity. If one of these fields rotates clockwise, the other rotates counterclockwise. In three-phase induction motors, currents with a 120° phase difference between them produce three alternating fields in the stator. If only the first harmonic of these three alternating fields is considered, six rotating fields are generated. Of these six, three rotate clockwise and the other three rotate counterclockwise, all at the same synchronous angular speed (ωs). When the three clockwise rotating fields coincide, the three counterclockwise rotating fields, which have a 120° phase difference among them, cancel each other out, resulting in a net zero value. Therefore, the motor rotates in the direction of the torque produced by the three coinciding clockwise rotating fields. At the moment voltage is first applied to the motor, the rotor is stationary. The rotating stator field cuts the stationary rotor conductors at synchronous speed ns, inducing an alternating voltage in the rotor. If the rotor were to rotate at synchronous speed, the stator field would no longer cut the rotor conductors, and no voltage would be induced in the rotor. Consequently, no current would flow in the rotor, resulting in zero torque. Therefore, induction motors cannot operate at synchronous speed. During operation, the rotor rotates at a speed lower than synchronous speed, and this speed varies with load. This speed difference is called slip. Slip is proportional to the difference between the rotor speed and the speed of the stator magnetic field and is usually expressed as a percentage. As the load on the induction motor increases, slip also increases. With increasing load, the rotor requires more energy to maintain alignment with the magnetic field, causing the rotor speed to decrease. As a result, the slip ratio increases.