motor VFD question

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petersonra

petersonra

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Semi-retired engineer
A customer wants to run a std NEMA GP motor at 50Hz/480V on a VFD.

I don't see any code violations.

Anyone see any issues code wise?

Whether the motor can take it is not my issue.
 
petersonra said:
A customer wants to run a std NEMA GP motor at 50Hz/480V on a VFD.

I don't see any code violations.

Anyone see any issues code wise?

Whether the motor can take it is not my issue.
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If the standard motor is rated for 60Hz/480V, then I see a problem running it at 50Hz/480V.
 
Besoeker said:
If the standard motor is rated for 60Hz/480V, then I see a problem running it at 50Hz/480V.
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IMHO, it depends on just how the VFD is set up. A sufficiently capable VFD could operate off 50Hz and provide 60Hz output to the motor if properly configured. In between, DC is DC.
The VFD would have to have its input rectifier circuit sized for 50Hz or else be oversized for the motor load.
 
GoldDigger said:
IMHO, it depends on just how the VFD is set up. A sufficiently capable VFD could operate off 50Hz and provide 60Hz output to the motor if properly configured.
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Didn't think that was the question.
But I could be wrong.
 
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Besoeker said:
If the standard motor is rated for 60Hz/480V, then I see a problem running it at 50Hz/480V.
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Not my problem if the motor cannot take it. Supposedly Siemens has been consulted and they may have blessed using the motor this way, although I am not privy to what they said and how it was phrased, or even what was actually asked, and it is not known to me just how this was handled.

It is a Siemens motor with three different ratings on the nameplate. I have seen the motor up close and personal and can verify the nameplate does actually say all this stuff.

one rating says 400V/275A/50Hz IE3
another says 480/60Hz/225A MC1
and the third says 480V/60Hz/275A IE3

It also says NEMA MG12-12 SF1.15 60Hz on another line. I think it also says TENV somewhere but that part is cut off in the picture I have and I can only see the "TE" part.

most of this is consistent with the motor datasheet that came from Siemens although there is additional information on the datasheet and some of what is on the nameplate is not in the datasheet.

at this point my plan is to tell our customer it is not a violation of the NEC or any other standard I can think of to run the motor this way. the actual motor side of it is just not in my scope.
 
GoldDigger said:
IMHO, it depends on just how the VFD is set up. A sufficiently capable VFD could operate off 50Hz and provide 60Hz output to the motor if properly configured. In between, DC is DC.
The VFD would have to have its input rectifier circuit sized for 50Hz or else be oversized for the motor load.
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the drive is 60Hz 480V in.

they want to run the motor at 50Hz/480V.
 
Besoeker said:
Not good.
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:thumbsup:
If they really need to run at 50Hz (to get the right shaft speed for example) then they would normally need to set the VFD up for 50Hz at 400 volts to keep the same V/F ratio.
If the motor were actually nameplated for 50Hz 480 volts, that would be because it is overbuilt for 60Hz 480 and the result should be OK.
But it is NOT.
one rating says 400V/275A/50Hz IE3
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Since that configuration would be installing the motor in a way that is not compliant with the manufacturer's instructions and is probably in violation of its UL or other listing, that would be a violation of the NEC as well, and it will be hard for the OP to disclaim that.
 
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I would point out a couple of things here.

First, this is a somewhat irregular situation.

Second, there is nothing that I can find in the code that actually prohibits this.

There is nothing in the code that says you cannot operate a motor in a way that may damage it long term. It just is not there.

As for operating it at a V/Hz ratio it is not designed for I would point out that it is very common to do this. It is what the boost setting in VFDs is for. If it is not code legal to use it, why would a UL listed motor controller allow such a setting?
 
petersonra said:
There is nothing in the code that says you cannot operate a motor in a way that may damage it long term. It just is not there.
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Unless you count 110.3(B). It may not apply here, I admit.
What about short term? :)
Just out of curiosity, do they have a credible reason for wanting to set the VFD output to 480V, or are they just trying to change as few things as possible on the assumption that that would somehow be better?
 
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We had the same situation in previous project, the available power was 400v,60hz & the cyclotron equipment (dedicated for proton therapy equipment) was german & made by Varian, their equipment either working in 400v,50hz or 480v, 60hz and they requested time to do their calibration to check what is the effect & finally they refused & the owner was obliged to provide additional transformer supplying 480v, 60hz.

Maybe, there are some differences in terms of using such critical equipment & the use of your VFD.
 
petersonra said:
I would point out a couple of things here.

First, this is a somewhat irregular situation.

Second, there is nothing that I can find in the code that actually prohibits this.

There is nothing in the code that says you cannot operate a motor in a way that may damage it long term. It just is not there.
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Long term.......at 20% above nominal voltage rating, maybe not so long.
 
ghostbuster said:
Is the motor inverter rated?
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Also not my problem. The motors are there. Changing them would be a problem, as would changing the drives. Big problem.

The reason for doing this is to try and get some additional HP out of the motor at 50 Hz. This suggestion came from the pump manufacturer. Apparently it is not an uncommon thing to do in Europe according to the pump manufacturer (European also).

The problem being encountered is that the drive goes into current limit at 50 Hz with the normal V/Hz curve. By increasing the voltage, they hope to reduce the current draw to the motor and keep the drive out of current limit.

I agree this is somewhat irregular, but that does not necessarily mean it is in violation of any code or that it is somehow unsafe.

It appears to me that this is more of a design decision than a code issue.
 
petersonra said:
The reason for doing this is to try and get some additional HP out of the motor at 50 Hz. This suggestion came from the pump manufacturer. Apparently it is not an uncommon thing to do in Europe according to the pump manufacturer (European also).
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Not something I've heard of. And we've put in hundreds of VSDs on pumps.

petersonra said:
The problem being encountered is that the drive goes into current limit at 50 Hz with the normal V/Hz curve. By increasing the voltage, they hope to reduce the current draw to the motor and keep the drive out of current limit.
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At 20%, it's too much. The motor will likely saturate and draw more current.


petersonra said:
I agree this is somewhat irregular, but that does not necessarily mean it is in violation of any code or that it is somehow unsafe.
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Might get hot enough to be unsafe.
 
Besoeker said:
Not something I've heard of. And we've put in hundreds of VSDs on pumps.


At 20%, it's too much. The motor will likely saturate and draw more current.
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according to the pump manufacturer it will draw less current at 480V/50Hz than for 400V/50Hz for the same HP required. makes sense to me.
 
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