# How Does Reducing Excitation Affect a Synchronous Induction Motor's Performance?

• Engineering
• Laa
In summary: The speed of a synchronous motor changes with excitation change because the number of rotations per minute (RPM) is directly proportional to the amount of power that is being supplied (this is because the speed of the motor is proportional to the frequency of the power supply).
Laa

## Homework Statement

(i) A star-connected, three-phase synchronous induction motor takes a current of 10 amps from a 415 volt supply at unity power factor when supplying a steady load. If the synchronous reactance is 5 ohms/phase and the resistance is negligible, draw the phasor diagram and calculate the value of the generated emf and the load angle.

(ii) If the excitation is reduced by 10% and, as a consequence the generated e.m.f. is reduced by 10%, calculate the new value of the generated e.m.f E, the stator current, the power factor and the load angle, assuming that the load does not change[/B]

## The Attempt at a Solution

For part (i) I have the emf calculated as 245V and the load angle as 11.6 degrees

I am struggling with part (i). I have the new emf at 220.5V but don't know where to go from there.

If I do the same equation for load angle as in part one it doesn't work.

Any help appreciated.

Hi Laa, welcome to PF!

Laa said:
I am struggling with part (i). I have the new emf at 220.5V but don't know where to go from there.
Since the load torque doesn't change and it's a 'synchronous' motor, what does that tell you about the active power drawn by the motor?

cnh1995 said:
Hi Laa, welcome to PF!Since the load torque doesn't change and it's a 'synchronous' motor, what does that tell you about the active power drawn by the motor?

Hi, thanks for the quick reply.

Not quite sure what you are getting at there but as the excitation has been reduced, power factor will be leading and the load angle will increase. The value of the stator current should remain the same

Laa said:
synchronous induction motor

By the way, that is wrong. Synchronous motors and induction motors are two kinds of motors. There is no such thing as synchronous induction motor. The problem is for a synchronous motor.
cnh1995 said:
Since the load torque doesn't change and it's a 'synchronous' motor, what does that tell you about the active power drawn by the motor?

Following up on that clue. How does the speed of a synchronous motor change with excitation change?

rude man
Laa said:
The value of the stator current should remain the same
Why?

## What is a synchronous induction motor?

A synchronous induction motor is a type of electric motor that operates by inducing a rotating magnetic field in its rotor through the use of an alternating current (AC) power source. It is commonly used in industrial and commercial applications due to its efficiency, reliability, and ability to maintain a constant speed under varying load conditions.

## How does a synchronous induction motor work?

The synchronous induction motor operates by utilizing the principle of electromagnetic induction. An alternating current in the stator windings creates a rotating magnetic field, which induces a current in the rotor windings. This current in the rotor then interacts with the rotating magnetic field, causing the rotor to rotate and produce mechanical energy.

## What are the advantages of using a synchronous induction motor?

There are several advantages to using a synchronous induction motor. These include high efficiency, low maintenance requirements, and the ability to maintain a constant speed under varying load conditions. Additionally, they can be easily controlled and are less expensive than other types of motors.

## What are the differences between synchronous and asynchronous induction motors?

One of the main differences between synchronous and asynchronous induction motors is their speed control. Synchronous motors operate at a constant speed, while asynchronous motors have a speed that varies with the load. Another difference is the type of current used; synchronous motors require AC power, while asynchronous motors can operate on both AC and direct current (DC) power.

## What are some common applications of synchronous induction motors?

Synchronous induction motors are commonly used in industrial and commercial applications, such as pumps, fans, compressors, and conveyor systems. They are also used in power generation, as they can operate at high speeds and are highly efficient. Additionally, they are used in appliances like refrigerators, washing machines, and air conditioners.

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