Types of Synchronous Motor

Depending upon the method of magnetization of the rotor, there are basically two types of synchronous motors:

Types of synchronous motor:

  1. non-excited
  2. Direct current excited

Let us discuss one by one

  1. non-excited

In this motor, the rotor these motor is constructed y steel. During its rotation at synchronous speed, it follows the synchronous rotating field in different steps, due to this it provides constant fields. 

Due to the field interaction of the stator with the rotor, it becomes an electromagnet and it has north and south poles that interact with stator field poles in this way rotor moves.

The rotor is made from such that has a high value for magnetization and demagnetization means it retentively is high.

It's again divided into three main  parts:
  • Reluctance motors
  • Hysteresis motors
  • Permanent magnet motors
In the reluctance motor, the rotor is made up of steel casting with the use of the projecting tooted poles. To minimize the torque ripples, the rotor poles are less than the stator poles. It contains squirrel-cage winding which is to provide starting torque to the rotor. Used in instrumentation applications.

Hysteresis motors are seld starting motor. This rotor is a smooth cylinder is made up of with the high coercivity magnetically hard cobalt steel. These motors are expensive and It is used where precise constant speed is required. It is generally used as servomotors.

In a permanent magnet synchronous motor, a permanent magnet is used along with steel for rotor design. They have a constant magnetic field in the rotor, so the induction motor winding cannot be used for starting time. It being used as gearless elevator motors.

         2. Direct current excited

The rating of DC motor is larger than one HP or one KW. The external direct current source is connected with the rotor of these motors for excitation.  This Dc source is connected with the motor by a rectifier circuit for rectification of supply.

The direct current at the rotor can is provided in two ways first one is by connecting ab external source and the second is by attaching a direct current generator with the shaft of the rotor.

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