# Why synchronous motor is a constant speed motor?

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The rotor of a synchronous motor moves at the same speed as the changing, rotating field in its stator. … This rotational speed will be constant with different mechanical loads, up to the point that the motor (or coupling) fails, hence it is a “constant speed” motor.

## What is a constant speed motor?

The American Institute of Electrical Engineers has defined the constant-speed motor as one the speed of which is either constant or does not materially vary; such motors are the synchronous motor, the induction motor with small slip, and the direct-current shunt motor. … Such a motor is called a normal-torque motor.

## Why the synchronous motor is not self started?

Above a certain size, synchronous motors are not self-starting motors. This property is due to the inertia of the rotor; it cannot instantly follow the rotation of the magnetic field of the stator. … Once the rotor nears the synchronous speed, the field winding is excited, and the motor pulls into synchronization.

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## How the speed of a synchronous motor is varied?

As you can see, the synchronous speed depends on the frequency of the supply and the number of poles of the rotor. Changing the number of poles is not easy, so we do not use that method. However, with the invention of solid-state devices, the frequency of the current fed to the synchronous motor can be varied.

## What is the advantage of synchronous motor?

The advantages of the synchronous motor are the ease with which the power factor can be controlled and the constant rotational speed of the machine, irrespective of the applied load. Synchronous motors, however, are generally more expensive and a d.c. supply is a necessary feature of the rotor excitation.

DC shunt motor

## Which DC motor has high torque?

DC Series motor has high starting torque. We can not start the Induction motor and Synchronous motors on load, but can not start the DC series motor without load. DC motor has high starting torque.In a series motor the same current flows through the armature and the field winding.

induction motor

## Which motors are not self starting?

The stator carries windings connected to an AC supply to produce a rotating magnetic field.At synchronous speedthe rotor poles lock to the rotating magnetic field, beacause of the constant magnetic field in the rotor these cannot use induction windings for starting. Synchronous motors are inherently not self starting.

## How does a synchronous motor start?

The motor is first started as a slip ring induction motor. The resistance is gradually cut-off as the motor gains speed. When it achieves near synchronous speed, DC excitation is given to the rotor, and it is pulled into synchronism. Then it starts rotating as a synchronous motor.

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## What is the speed of synchronous motor?

Rotor speed will be 1/6 of that experienced with a 2-pole synchronous motor. Example: 60 Hz would rotate a 2-pole motor at 3600 rpm, or 600 rpm for a 12-pole motor.

## Where do we use synchronous motor?

Synchronous motors are normally used in applications in which a constant and precise speed is required. Typical applications of these low power motors are positioning machines. They are also used in robot actuators. Synchronous motors are also used in ball mills, watches, record players, and turntables.

## What is field current in synchronous motor?

The field current may be supplied from an externally controlled rectifier through slip rings, or, in larger motors, it may be provided by a shaft-mounted rectifier with a rotating transformer or generator. A synchronous motor with only a field winding carrying a direct current would not be self-starting.