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Synchronous Motors: Areas of Application and Advantages and Disadvantages

Jun. 23, 2021

A Synchronous Motor is a type of AC motor in which the speed of rotation of the shaft is the same as the frequency of the applied current. In other words, a synchronous motor works in the same way as an AC motor, with the difference that the total number of revolutions of a synchronous type shaft is equal to an integer multiple of the frequency of the applied current.

The operation of a synchronous motor does not depend on the induction current. In this type of motor, unlike induction motors, there are multi-phase AC electromagnets on the stator that generate a rotating magnetic field. In synchronous, the rotor consists of permanent magnets that are synchronized with the rotating magnetic field and rotate synchronously with the frequency of the current applied to it.

Synchronous Motor

Synchronous Motor

Applications of synchronous motors include:

The basic use of synchronous motors is "power factor correction", which means improving the power factor of a system.

Synchronous motors are used for voltage regulation

Synchronous motors are generally used for low speed, high power loads.

Synchronous motors are typically used in air and gas compressors and vacuum pumps.

Synchronous motors can also be used in crushers, mills and grinders.

They are also used for exhausters, fans and blowers.

Advantages of synchronous motors include:

The advantage of using synchronous motors is that the power factor can be controlled. Over-excited synchronous motors have an over-excited power factor and operate in parallel with induction motors, thereby increasing the system power factor.

The speed remains constant regardless of the load in the synchronous motor. This quality helps industrial machines, which require constant speed regardless of load.

Synchronous motors have a wider air gap than Induction Motors, which makes them more mechanically stable.

The electromagnetic power varies linearly with the voltage in a synchronous motor.

Synchronous motors typically operate at higher efficiency than induction motors, especially at lower speeds.

Disadvantages of synchronous motors include:

Synchronous motors require DC excitation from an external power source.

These motors are not self-starting motors and require some external device to start and synchronize them.

The cost per kilowatt output is typically higher than that of induction motors.

The speed cannot be adjusted unless the input power frequency is adjusted.

They cannot be started with a load because it has zero starting torque.

Collector rings and brushes are required, which results in high maintenance costs.

Synchronous motors are not suitable for applications that require frequent starting of the machine.

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