How is the Conversion factor (V/f) used in VFD?

In the VFD drives the ratio of V/f remains constant.so by changing frequency you can set the voltage flucations..........

Hope this would helps.........

Excuse my ignorance- what is VFD?

What that system is used for ?

VFD = Variable Frequency Drive.

This is usually used (and very frequently nowadays) for controlling the motor speed.

It has also (hence) the capability to start the motors.

It does its activity by changing the line frequency of the AC current.

Yes,that is used in the new laundry washing machines.

Do you have some idea about circuit theory of that drive ( circuit board) ?

Thanks, I appreciate this response.

Furthermore, if (V/f) changes and causes a change in magnetic flux, will that affect the current within the motor?

Almost in all cases yes. however the VFD will ensure that you do not cross the limit.

It is like this.

The power

P = VICosΦ or √3VI CosΦ (3 phase)

The speed of the motor (as controlled by VFD will be at the the slip speed) and hence we will not consider the other high slip phenomenon.

At different speeds, obviously the load will demand different power.

if it is a resistive load - the power of course will be linear with voltage

If it is pump then you have to look at the pump characteristics, and its power requirement at different RPMs (Operating characteristics as I mentioned earlier).

Similarly any load will have its own typical OCC (operating characteristics curve)

In normal motor what we do overlap the load OCC with motor curve. The intersection of OCC with motor curve will provide the operating point (slip and thus RPM, power, power factor, ...)

here we will neglect the slip for simplification (or in fact will go for the slip at the maximum power condition) and then calculate the load for each RPM (Watts, KWs) and then go back and based on motor efficiency calculate the current for each RPM (and from there based on slip to frequency)

This will provide you approximately the I-f characteristics for the motor-load combination.

However there is a good possibility that the current for a particular load- a few not very common loads are there, (but that is only if the system is improperly designed) will cross the rated current. Any good VFD if married well to the system will trip/ control the current in these condition, and in either cases most likely the motor will stall.

Secondly you must remember that the current carrying capacity of the conductors (stator) are much higher at low frequencies - lower skin effect.

And manipulating all these, and also a few other factors, the VFD drives are able to provide 1.5 times or even more torque at lower frequencies (this characteristics of having very high starting torque in AC Motor is not available in any other starting mechanism)

Thank you once again.

This is absolutely clear to me.