can anyone supply details on using an synchronous induction motor to improve power factor please?

Question

I am led to believe that mines use this system, using the "pit head fan motor" to improve the P.F. for the rest of the pit.

Answer 1

Yes mines do use the mine fan to correct power factor for the mine. This is the way it works. When you synchronise the motor, i.e. put a D.C. supply to on to 'lock' the rotor at synchronous speed (no slip) you can alter the excitation to run the motor at a leading power factor which offsets the lagging power factor caused by the rest of the induction motors at the mine.

Answer 2

Actually Max has mis-interpreted the question.
A synchronous condenser is a synchonous motor operating on no load..... The questioner was asking whether a synchonous motor can be used to improve the PF.
So the answer is a definite yes over or under exciting a synchronous motor ie a synchronous motor driving a load such as a fan/compressor/pump etc. can bring the PF back to unity.

Definition: over exciting the motor is raising the excitation volts above the line volts
Under exciting the motor is reducing the excitation volts to below the line volts....

Source: Electrical Engineer with 50 years experience

Answer 3

The answer 'max' gives above is one correct way of going about power factor correction. I believe they still sell synchronous motors specifically for pf correction, and they act like a capacitor bank in terms of reactive power generation.

If you have a constant speed mechanical load, then a synchronous motor can be used to drive it. You then set the motor field current high enough such that it is over-excited (leading power factor). I suppose you would want to set the field current all the way up to rated if you have a lot of running induction motors or other lagging power factor devices around. That depends on your situation though, as the second answer indicates.

So, in a nutshell. Yes, a synchronous motor can improve your power factor. It can operate under-excited (lagging pf) or over-excited (leading pf) depending on how you set the field current.

Answer 4

power factor correction.

Usually calculate the capacitance to add in to your circuit. An induction motor may supply a specified capacitance and can thus correct the power factor.

The induction motor can change the PF in a circuit in many ways, you will truly need to calculate the circuit. There are just to many possibilities to be able to give you a cook book method, as it all depends on the circuit elements themselves.

Basically I would look in a text (such as ISBN 0-534-95367-0)
The power factor is the "phase angle", where current is either Leading or Lagging. This is the angle between the voltage and the current.

Answer 5

you can improve PF using a synchronous condenser.
A synchronous condenser is fundamentally an AC synchronous motor that is not attached to any driven equipment. Its field is controlled by a voltage regulator to either generate or absorb reactive power as needed by the system.

When over-excited(at no load),synchronous motor runs with leading power factor ( with lagging power factor when under-excited)