Synchronous vs Induction Motors: A Comparison Guide

To compare synchronous and induction motors, one must understand some key characteristics that describe their performance and behavior. These include the rotational speed of the motor, measured in revolutions per minute (RPM). Synchronous motors have a fixed speed that depends on the supply frequency and the number of poles, while induction motors have a variable speed that depends on the slip. The rotational force of the motor is measured in newton-meters (Nm) or pound-feet (lb-ft), with synchronous motors having a constant torque that is independent of the load, and induction motors having a variable torque that depends on the load and the slip. The mechanical output of the motor is measured in watts (W) or horsepower (HP), with synchronous motors having a constant power that is proportional to the torque and the speed, and induction motors having a variable power that is proportional to the torque and the square of the speed. Lastly, power factor is the ratio of real power to apparent power, which indicates how efficiently the motor uses electrical energy. Synchronous motors have a high power factor that can be adjusted by changing excitation current, while induction motors have a low power factor that decreases with load and slip.

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Advantages and disadvantages of asynchronous motors

Asynchronous motor vibration and noise Asynchronous motors are widely used mainly because of their advantages: simple structure, reliable operation, easy manufacture, low price, ruggedness, high efficiency and quite good working characteristics.

The main disadvantage of asynchronous motors is that it is not economically smooth in a wide range and that it must absorb the lag of reactive power from the grid. In the motor, the main magnetic flux enters the air gap substantially in the radial direction and generates a radial force in the stator and the rotor, thereby causing electromagnetic vibration and noise. At the same time, tangential moment and axial force are generated, causing tangential vibration and axial vibration. In order to calculate the electromagnetic noise of the motor and analyze and control these noises, it is necessary to know the source of these noises and vibrations, that is, the force waves that generate vibration and noise. At present, the magnetic field of the motor can be calculated by CAE simulation analysis.

The vibration of the motor is the most concerned issue in the current motor structure design, which consists of three parts: electromagnetic vibration, mechanical vibration and gas vibration.

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Electromagnetic vibration: It is the interaction of the magnetic field in the air gap of the motor, which produces electromagnetic force that changes with time and space on the rotor and stator, causing the motor to vibrate.

Mechanical vibration: Vibration caused by mechanical imbalances such as rotor imbalance, bearings, etc.

Gas vibration: Vibration caused by air flow or aerodynamic forces in the ventilation components of the motor.

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