480 volt vfd with 230 volt electric motor

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NDRED

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North Dakota
I have 480 volt single phase power and need to run a 230 volt 3 phase submersible pump motor (can't re-wire it for 460 volt). I would like to use a 480 volt vfd and program it to match the 230 volt motor nameplate info. In theory if everything is programmed into the vfd correctly the drive should feed the motor the appropriate current/voltage to operate correctly.
The drive would be de-rated for the single-phase power coming into the drive, so the inverter side of the drive would be sized appropriately to handle the higher amp draw of the motor.


I think in theory this should work fine, but would like to know if I'm missing something that would cause this not to work.
 

LEO2854

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I have 480 volt single phase power and need to run a 230 volt 3 phase submersible pump motor (can't re-wire it for 460 volt). I would like to use a 480 volt vfd and program it to match the 230 volt motor nameplate info. In theory if everything is programmed into the vfd correctly the drive should feed the motor the appropriate current/voltage to operate correctly.
The drive would be de-rated for the single-phase power coming into the drive, so the inverter side of the drive would be sized appropriately to handle the higher amp draw of the motor.


I think in theory this should work fine, but would like to know if I'm missing something that would cause this not to work.

How does the VFD create 3 phase? I have not played in one for about 15 years.

Welcome to the forum....:)
 

NDRED

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Location
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As I understand it the vfd takes ac power, rectifies it into dc power than inverts the dc power back into three phase ac power to run the electric motor. The drive can rectify three phase power the same as single phase power into dc current, after that the inverter side of the vfd re-creates three phase power to run the motor. The key is the drive must be de-rated / sized appropriately to handle the missing conductor/phase coming into the drive

We do this a lot with 240 volt single phase to run 230 volt three phase motors. Just have never used one to take 480 volt and run a 230 volt motor...
 

GoldDigger

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The VFD cannot deliver a lower pulse voltage than the rectified peak of the input voltage. It can deliver any desired RMS voltage by varying the duty cycle of the pulse.
So thermally the motor is not being overdriven, but the peak voltage on the insulation and the mechanical stress on the winding will be twice the design level.
Given that some motors have problems even with a matching nominal voltage VFD, I would not be comfortable with the suggested solution without more information about the motor.
 

NDRED

Member
Location
North Dakota
Motor is 15hp, inverter rated franklin electric motor. The motor is located 30ft from the drive, so the compounding pulses shouldn't be a problem...

I agree using a transformer would definitely work. Just makes things more expensive. wouldn't be a deal breaker by any means just would prefer not to use a transformer.

Getting a 460 volt motor would be the best, but isn't an option in this case.
 
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Jraef

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The VFD cannot deliver a lower pulse voltage than the rectified peak of the input voltage. It can deliver any desired RMS voltage by varying the duty cycle of the pulse.
So thermally the motor is not being overdriven, but the peak voltage on the insulation and the mechanical stress on the winding will be twice the design level.
Given that some motors have problems even with a matching nominal voltage VFD, I would not be comfortable with the suggested solution without more information about the motor.
Bingo. The motor insulation is not likely capable of taking the stresses of the +650VDC pulse voltage, even without the added stress of reflected waves, which, but the way can happen even at 30ft. If you can get, from Franklin, assurances that they used inverter duty magnet wire in their windings, rated at 1600V or higher, then it should be OK.
Motor is 15hp, inverter rated franklin electric motor. The motor is located 30ft from the drive, so the compounding pulses shouldn't be a problem...

I agree using a transformer would definitely work. Just makes things more expensive. wouldn't be a deal breaker by any means just would prefer not to use a transformer.

Getting a 460 volt motor would be the best, but isn't an option in this case.

The rub is, when you raise this issue with Franklin, they will likely tell you that you cannot use a VFD at all, unless it is theirs (they are like that) without voiding the warranty on the pump. If the pump is already out of warranty anyway, no problem, although they may not give you an answer.

Here's what I would do. Buy a dV/dt filter (not just a reactor) for the load side of the VFD, then try it. All you need to do is program the VFD to reach 240V at 60Hz and it should do wht you want. We do it all the time for demo units. But the difference is, we don't run them much, and probably more importantly, we don't buy the motors, the factory does. So no skin off my nose when I smoke a motor. And by the way, I've gone through two motors in 3 years (no dV/dt filters).
 

Rampage_Rick

Senior Member
Presumably you don't need to adjust the speed of the VFD, you just want it to chug along at 60Hz

As others have mentioned, a VFD fed with 480V AC will have a bus voltage around 650V DC so you might have some issues with that. I'm most familiar with the older AB 1336 Plus drives and I believe they can be programmed to output as low as 25% of rated voltage. The output voltage is usually a slope anyways, not full voltage through all frequencies.

Sizing the VFD to convert from 1ph to 3ph is also pretty straightforward. Basically talke the FLA rating of the motor and multiply by 1.73, then pick a VFD with at least that many amps. Keep in mind that addtional derating may be necessary due to altitude or other factors (I know the 1336 Plus have to be derated above 3000 ft because the thinner air doesn't cool as efficiently)
 

Jraef

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...

Sizing the VFD to convert from 1ph to 3ph is also pretty straightforward. Basically talke the FLA rating of the motor and multiply by 1.73, then pick a VFD with at least that many amps. Keep in mind that addtional derating may be necessary due to altitude or other factors (I know the 1336 Plus have to be derated above 3000 ft because the thinner air doesn't cool as efficiently)
Just a slight difference in opinion on the sizing. The 1.732 factor has to do with the sizing of the diodes in the rectifier only, because all of the 3 phase power must go through 4 diodes instead of all six, so the current through them increases by the sq. rt. of 3 (1.732).

But... That's not the whole story. The DC bus capacitors must now smooth a much higher amount of DC bus ripple created by the lower pulse rate coming from the rectifier, plus the ripples will now dip all the way to the zero V level, whereas with a 3 phase full 6 pulse bridge, that never happened. To counter that problem, you need more bus capacitance, even more that you would get with the 1.732 derate. So the generally accepted derate is at least 50% (2x the 3 phase motor current), but with a corresponding derate on the ambient temperature to 25C (77F), because the capacitors will run hotter. You can usually use a 65% (3x the 3 phase motor current) if you need the same ambient rating for the VFD, typically 40-50C (104-122F). On an outdoor pump panel retrofit, if this is what you are doing, I would not skimp on derate factors unless the VFD mfr says otherwise in writing (most will not), or you will likely regret it. If the drive is in a climate controlled room, 50% is OK.
 

winnie

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Springfield, MA, USA
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Electric motor research
I don't think anyone uses different magnet wire insulation for 230V and 460V motors, so running a 230V motor with a 480V inverter _shouldn't_ be a problem.

But the other side of the coin is that you should reconsider the line 'Getting a 460 volt motor would be the best, but isn't an option in this case. ' You have to have _some_ way of replacing/repairing the motor, so everything that you do to use the motor at 230V has to be considered in light of the cost of using the higher voltage motor. If (for whatever reason) this motor is very expensive to repair/change, then your drive costs should include carefully protecting the motor from damage.

If you go the transformer route, then you should probably still consider using the dV/dt filter that Jaref suggests. Also, you can put the transformer on the output of the VFD, to match the voltage of the 480V VFD to the motor, and add filtering.

-Jon
 

GoldDigger

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Does any VFD manufacturer support putting a transformer on the load side?
If nothing else the performance of the transformer core at the high harmonic level involved would be problematic.
Using an air core pulse transformer maybe? :angel:
 
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mike_kilroy

Senior Member
Location
United States
I don't think anyone uses different magnet wire insulation for 230V and 460V motors, so running a 230V motor with a 480V inverter _shouldn't_ be a problem.

I wouldn't bet my job on that line. I personally know one company that DOES use lower voltage wire. I have personally smoked more than one of theirs in less than 5 minutes running no load.

Put a 2:1 step down xfmr on INPUT side of a 230v vfd and do it right.
 

Jraef

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I don't think anyone uses different magnet wire insulation for 230V and 460V motors, so running a 230V motor with a 480V inverter _shouldn't_ be a problem.

But the other side of the coin is that you should reconsider the line 'Getting a 460 volt motor would be the best, but isn't an option in this case. ' You have to have _some_ way of replacing/repairing the motor, so everything that you do to use the motor at 230V has to be considered in light of the cost of using the higher voltage motor. If (for whatever reason) this motor is very expensive to repair/change, then your drive costs should include carefully protecting the motor from damage.

If you go the transformer route, then you should probably still consider using the dV/dt filter that Jaref suggests. Also, you can put the transformer on the output of the VFD, to match the voltage of the 480V VFD to the motor, and add filtering.

-Jon
I agree with you, except that 99.9% of Franklin pumps sold are submersible well pumps. So those are NOT standard off-the-shelf NEMA motor designs, in fact they are so specialized that Franklin actually makes the long slender motors for other submersible pump mfrs. Every one of them is a basically custom design for this use and they use what they use as far as magnet wire. They are all single voltage as well, not 230/460 like most off-the-shelf NEMA motors (although they have 6 lead Y-Delta versions on special order).

I will say though that I missed seeing that this IS an "inverter duty" submersible pump. No details on Franklin's site explaining exactly what that means, and there is no "official" definition of that marketing term, but most of the time it means they used the higher voltage magnet wire. All Franklin says is "All models variable frequency drive (VFD) approved". But you should also read this:
http://www.franklin-electric.com/media/documents/60Hz_AIM_40-41.pdf


Transformers after the VFD: this is done a lot in MV applications where people don't want to buy MV drives, so they buy LV drives and use a step-up transformer for the MV motors. I have always taken the word of much more intelligent transformer manufacturing engineers who have always told me that it takes some special attention on the core steel used in the design to keep the harmonics from increasing the hysteresis losses in the transformer, but I have been chastised over and over from people insisting that this is all BS from the transformer people who just want to sell more expensive transformers. I'm not going to pretend I know enough about transformer design to say which is right, but I do know that on all the ones I did with custom transformers (that I am still aware of), not one suffered a transformer meltdown. Did others that used standard transformers melt down? I have no idea, I never did one.
 

Rampage_Rick

Senior Member
Just a slight difference in opinion on the sizing. The 1.732 factor has to do with the sizing of the diodes in the rectifier only, because all of the 3 phase power must go through 4 diodes instead of all six, so the current through them increases by the sq. rt. of 3 (1.732).
I got worried there for a second, had to pull out some specs. Working on a project to swap a 1PH 215TC 10HP motor for a 3PH 215TC 10HP motor to gain pump pressure control. Had it worked out to use an existing 1336S-A015 drive. Motor is rated 23.8 FLA @ 240V and drive is rated 48A. So in my case I should be OK with a 15HP drive for a 10HP motor.
 

Besoeker

Senior Member
Location
UK
Does any VFD manufacturer support putting a transformer on the load side?
If nothing else the performance of the transformer core at the high harmonic level involved would be problematic.
Using an air core pulse transformer maybe? :angel:
I've done it on some 800kW drives.
I used an iron cored transformer that had an air gap.
Worked fine.
 
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