Sine Wave/Periodic/Variable Frequency Power

It depends upon how closely the variable frequency power from the equipment in question approaches a sine wave, and there are standards for this sort of thing; in general, if it is CE-marked and therefore pan-EEC compatible, the approach is a good one and will make very little difference.

Thanks for your ans PWSlack:

Lets say if the sine wave is converted to variable frequency by VFD then supplied to motor.

My question is what difference will it make in motor behaviour if variable frequency power is 50% match of sine wave or 90% match of sine wave?

whats the need of converting the sine to variable?

I came up with this question because I read that when VFD is used in front of motor, the supply gets converted into variable frequency power. Whats the need of converting? I dont know, what difference will it make if motor is fed with 2 different kinds power supplies.

Thanks,

What big factor controls the rpm of the motor? If we change that can we not change rpm(speed).

I am not asking about changing the speed of the motor.. I simply asked if someone has any idea of how a motor will behave with these two different power supplies.

If you do not need to change the speed of the motor - then why in hell are you using a VSD (VFP)?

VSD are designed to provide you with a sinusoidal output at a specified frequency - which is the best and most efficient for for motors.

If you are in INDIA and are subjected to typical frequency variations of 49 - 51 Hz, . . . and you are operating a paper mill where the speed of the motors is required to be much better than +/-0.1%, . . . then you would use a VSD to provide the required frequency stability and motor speed stability required.

The straight answer is that, all other things being equal, the speed of an AC motor is directly related to the frequency of the AC voltage applied to its terminals, and is therefore fixed to a small range off of the power line frequency.

A VFD (Variable Frequency Drive) or VSD (Variable Speed Drive) varies the frequency of the sine wave that the motor sees and adjusts its speed accordingly "fooling" the motor into operating at speeds it that its physical configuration, the number of poles, wouldn't normally allow.

Study this formula: Synchronous speed = (120 x line frequency) / number of poles.

Since the number of poles is fixed, the only variable is the line frequency at its terminals, the VFD or VSD varies this to change the speed. If you're thinking anything other than an ordinary AC motor than you should read this.

Thank you so much for this explanation. You really got down to my level to make me understand. Thanks much!!

One way is with an oscilloscope.

Variable frequency and sine wave are not mutually exclusive. If the VFD outputs a true sine wave, it (or its literature) will probably say so. If not, there will be increased harmonic noise from abrupt "corners" in the waveform.

Yeah, I don't think the original concept of a VFD was quite what was getting through to the OP.

Thank you so much Trecou!!

Your answer was the best !!