# How the speed of a synchronous motor is varied?

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Synchronous motors are constant speed motors. … However, with the invention of solid-state devices, the frequency of the current fed to the synchronous motor can be varied. We can control the speed of the synchronous motor by changing the frequency of the supply to the motor.

## Why does the speed of a synchronous motor remain constant even under variable load?

Originally Answered: why does speed of synchronous motor remain constant even under variable load? the stator and rotor magnetic field will get locked at an angle, that angle is called as load angle or torque angle. so if load increases the angle between the two fields will also keep increasing with speed as constant.

## What are the various methods for speed control of synchronous motor?

 There are essentially two control modes for synchronous machine drive:  Open loop, true synchronous mode  Close loop, self control mode  In open loop contol mode, the motor speed is controlled by independent frequency control of the converter.

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## Why a synchronous motor is a constant speed motor?

The rotor of a synchronous motor moves at the same speed as the changing, rotating field in its stator. The rotor’s magnetic field is “synchronized” with the stator’s field. … Their speed is dependent on the number of poles and the supply frequency. They have a constant speed at a given supply frequency.

## When speed is changed in a synchronous generator?

The only way that an in increase in electrical load can decrease speed is if the load is greater than the generation. So, if the load is 20MW and the frequency is stable, if the load increases to 21 MW (actually any value above 20MW) and fuel is not increased then the speed (and the frequency will decrease).

## Will increase in load the speed of synchronous motor?

Thus, if the load on a synchronous motor is increased the following points are considered which are given below. The motor continues to run at synchronous speed. The torque angle δ increases. … The phase angle ϕ increases in the lagging direction.

## Can we change the speed of synchronous motor?

Synchronous motors are constant speed motors. … However, with the invention of solid-state devices, the frequency of the current fed to the synchronous motor can be varied. We can control the speed of the synchronous motor by changing the frequency of the supply to the motor.

## What is synchronous speed?

: a definite speed for an alternating-current machine that is dependent on the frequency of the supply circuit because the rotating member passes one pair of poles for each alternation of the alternating current.

## 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.

## What is the formula for synchronous speed?

The synchronous speed of an AC motor is determined by the frequency of the source and the number of poles. The RPM is calculated by multiplying the frequency times 60 and dividing by the number of pairs of poles. This was explained in Chapter 6. Some motors are designed to operate at synchronous speed.

## What is the constant speed motor?

This motor combines a power on activated type clutch and brake with an induction motor. It is ideal for high-frequency starting and stopping. … Suitable for applications where the motor is operated starting, stopping and reversing repeatedly and the motor is operated at synchronous speed regardless of load torque.

## What is the working principle of synchronous motor?

The principle of operation of a synchronous motor can be understood by considering the stator windings to be connected to a three-phase alternating-current supply. The effect of the stator current is to establish a magnetic field rotating at 120 f/p revolutions per minute for a frequency of f hertz and for p poles.

## 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.

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## How do you control the speed of a synchronous generator?

The synchronous machine speed is controlled by varying the frequency. Speed control of synchronous machine is achieved by voltage fed inverters, current fed inverters or cyclo converter. Speed control is of two types I.e. scalar control and vector control.

## Why the synchronous motor is not self starting?

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.

## Is a synchronous generator AC or DC?

A DC generator is a device that converts mechanical energy into DC power. … Synchronous Generator, that is, an alternator (AC generator) with the same rotor speed as the rotating magnetic field of the stator. According to the structure, it can be divided into two types: rotating armature and rotating magnetic field. 