460V VFD running a 230V motor 2

[Barry1961]

Due to a mix up a customer has several 1/10 hp, 230 volt, 3 phase, 60 Hz motors and 460 volt 1/4 hp VFD's. The motors are 50-60 feet away from the VFD's.

They have tried "reducing the voltage with the VFD" and have burned a couple of motors. I am getting this information second hand.

If you can run a 230V motor with a 460V VFD, what would be the proper procedure? Would you recommend reactors?

I am guessing that just using a single phase, 277V, would trip on under voltage.

Barry1961

 

[Marke]

Hello Barry1961

In theory, you can adjust the output of the VFDs down to 230V and this will run the motor, but the problem is that although the average voltage is 230 volts, this is made up of a switched waveform with a low mark space ratio. The switched voltage will still be in the order of 600 - 700 volts.
The 230 volt motors would have adequate insulation for 230 volts, but not necessarily for the 600 - 700 volts.

If you use the VFDs with the output voltage set to 230 volt at rated frequency of the motors, and you use a sinusoidal filter on the output of the VFD, there should not be any major issues.

Best regards,

Mark Empson

http://www.lmphotonics.com

 

[davidbeach]

Put a 480 - 240V transformer between the drive and the motor?

 

[Marke]

Yes, this would work but would result in increased flux reductions at low frequencies which may or may not be an issue depending on the application.

Best regards

Mark Empson

http://www.lmphotonics.com

 

[torslum]

You should also pay attention to the output frequency; if running in open loop, you would most probably get a reduced frequency at 230V (when your drive is 460V) unless you have programmed the drive correctly.

The U/f-ratio should be correct, and you can usually program this in your drive. The U/f-ratio doesn't matter for the VFD itself, but it is very important for the motor. So you should have 230V@60Hz set as parameters.

The 460/230-ratio is 2, so unless it is specified your drive might set out approximately 230V and 30Hz (as it might believe you still want to have 60Hz at 460V). This would be very bad for the motor, as the 230V@30Hz would lead to severe overfluxing for a motor with 230V@60Hz nameplate.

I don't know what has been tried and checked already, but this would be an important issue if it is not implemented.

 

[Barry1961]

I have noticed that smaller motors, like the 1/10 hp, are more likely to fail when running on a 460V VFD. In the past this has been solved by putting filters on the output of the VFD.

Roughly, what would the peak voltage be at 60 hertz on the output of the sinusoidal filter with the VFD set at 4 volts per hertz and a 460 volt input?

Barry1961

 

[DickDV]

Barry, that depends entirely on the effectiveness of the filter. If, for example, the filter was a sine filter with 100% effectivity, the the highest voltage the motor would see is exactly the same as a pure sine wave, the same as if it was connected across-the-line. Peak voltage on a 240V sine wave would be 339V.

It is unlikely that the filter would actually be 100% effective so some pulses would get thru. These would be higher than 339V but less than the 660V pulses the drive is sending out.

One reason small motors sometimes run without trouble at 230V on 460V supplied drives is that, even tho they are wired for 230V, they are would dual voltage 460/230. These motors are not usually at risk. Motors that are wound for a single supply voltage, ie. 230V, are at risk and would need filtering.

At these small horsepowers, I would forget the filters, buy a 460/230V transformer with a 230v drive and do the job properly. In addition, the transformer greatly reduces potential problems with common mode noise, input harmonics, etc. etc.

 

[jraef]

One thing that you didn't state is what is the input line voltage? You said it was a 460V drive, but are you feeding it 480V or 240V? If you are feeding it with 480 now, putting a transformer on the line side may not work because most drives do not have a wide enough voltage range to get down to 240V.

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[Barry1961]

The line voltage is 460 volts.

Barry1961

 

[akselj]

You can not use a transformer between the VFD and the motor as the output is not a sinus wave, the losses in the trafo will be very high.

Aksel

 

[Marke]

Hello akselj

I disagree, you can use a three phase transformer on the output of the drive. The induction motor is esentially a short circuited transformer.
I would recommend a delta / star configured transformer to cancel some harmonics at the same time.

Best regards,

Mark Empson

http://www.lmphotonics.com