VFD ideas for single phase to 3 phase 240 3HP

[kwired]

UPDATE:
So I got the ABB drive and got intouch with the motor manufacturer as they still make this motor.
And they said that since the motor is from the 70's its too old to run on a VFD and presumably I should buy a new motor.

Now my plan is not to use any VFD features, just as a phase converter, set it at 1200 RPM.
I plan to have it be triggered with an icecube relay, where the coil of the icecube is powered by the existing 120V controls.
Any thoughts/ experience on using a VFD with an old motor, like 40 years old?

Thanks all

The problem is the insulation rating in the motor. If you are running it at 240 instead of 480 your troubles will be less.

Also as mentioned a line reactor between the drive and the motor will lessen the peaks that are going to be damaging to the motor insulation. This possibly not even much concern for 240 volt operation but likely would be a must for 480 volt operation.

 

[ptonsparky]

I don't think it will matter if you use the "features' of the drive or not. The peaks will be there anyway but as Kwire says, they most likely won't be high enough anyway @ 240 volt.

 

[synchro]

A Load reactor is supposed to help.

The harmonic and other high frequency content from a VFD also puts thermal stresses on a motor due to hysteresis and ohmic losses, and a load reactor could reduce this effect:

Load Reactors

Load Reactors

www.galco.com

If a new replacement motor is easily available though, that should be seriously considered.

 

[garbo]

The problem is the insulation rating in the motor. If you are running it at 240 instead of 480 your troubles will be less.

Also as mentioned a line reactor between the drive and the motor will lessen the peaks that are going to be damaging to the motor insulation. This possibly not even much concern for 240 volt operation but likely would be a must for 480 volt operation.

At a large hospital that I retired from they added VFD'S to almost every motor above 3 HP. A lot of the motors were the original ones from the early 1970's when the building was built. Never had trouble with burning out old motors. They had line reactors on every line side of drives and for some reason something between the drive & motor on maybe 40% of drives. We always purchased energy saving drive rated replacement motors. On a new 12 story halve a billon building they used 18 pulse drives on all motors above 40 HP except for soft start on 200 HP fire pump. I talked to techs from Danfoss & ABB and none of them liked the 18 pulse drives. They had two 1750 HP chillers on drives that had their own 13,200 feed to a 4,160 volt step down transformer that ran the 4,160 volt motors.

 

[tortuga]

Thanks all for the replies.
Ill be looking into a load reactor and getting a quote on a new motor.
The machine is now in a prototyping shop so wont be in heavy 24/7 production floor use anymore.
Hence the need to convert from 480 to 240 single phase.
Turns out the machinist in there has done this to all the other old mills, drills and lathes in there.

 

[LarryFine]

As long as you have to replace it anyway, is there any chance of getting a 1ph motor?

 

[Jraef]

Rueland motors are general highly custom, that's their specialty, so a replacement may not be as easy as you might think.
but a load reactor is the minimum I would add, maybe even a DV/DT filter. I always say that you might as well use whatever life it has left rather than pre-emptively replace it.

 

[tortuga]

Thank you all for your input, I picked up the load reactor today.

As long as you have to replace it anyway, is there any chance of getting a 1ph motor?

It *might* move back to production so id hate to do that then get the call...
Were not into the ABB VFD very much at this point, its a special single to three phase VFD so wont be of any use if it moves again...
And I dont think Rueland offers anyhting in single phase.

Rueland motors are general highly custom, that's their specialty, so a replacement may not be as easy as you might think.
but a load reactor is the minimum I would add, maybe even a DV/DT filter. I always say that you might as well use whatever life it has left rather than pre-emptively replace it.

Highly custom indeed, I get that now.
OK what is a DV/DT filter?
Thanks all

 

[tortuga]

Found this

https://www.eaton.com/content/dam/eaton/products/low-voltage-power-distribution-controls-systems/motor-contols/vfd-dvdt-filter-ap043001en-application-note.pdf

Edit it says
" For a 240 V motor, the reflected wave
would be closer to 680 V, so a dV/dT filter would
not be required; however, a load reactor is always
recommended."

 

[Besoeker3]

OK what is a DV/DT filter?
Thanks all

“dv/dt” is one borrowed from calculus, meaning the instantaneous rate of voltage change over time
I've used 1000V per us.

 

[winnie]

Highly custom indeed, I get that now.
OK what is a DV/DT filter?
Thanks all

The 'reflected wave' issue is what is known as a transmission line effect, and is seen when you have electrical wavelengths similar to your cable length.

For a 100 foot cable to a motor you would need frequencies on the order of 10 MHz to see transmission line effects, but the drive frequency of the motor is perhaps 60Hz and the pwm switching frequency is perhaps 2 kHz, so what gives?

The rapid switching is itself a source of harmonics, extending to many multiples of the pwm frequency, how high being a function of how rapid the switching event is. Perfect square wave switching has harmonics out to infinity (which is why you cannot have perfect switching).

A dv/dt filter slows down the switching transitions to reduce the pwm harmonics so that you are less likely to see transmission line effects.

Having the VFD near the motor will also reduce these effects.

Jon

 

[tortuga]

Thanks all for breaking it down, good info.
When I here 'filter' I think capacitor and resistor combo, like a 'snubber' on a relay circuit.
The load reactor appears to be just a coil.
In this particular machine the VFD to motor will be about 5-6 foot conductor run @240V.

 

[zbang]

When I here 'filter' I think capacitor and resistor combo, like a 'snubber' on a relay circuit.
The load reactor appears to be just a coil.

The simplest electronic filters are made from only a reactive and a resistive component. Sometimes it's an RC (resistor/capacitor), sometimes it's an RL (resistor/inductor). (And sometimes the R part is a wire.)

 

[kwired]

Found this

https://www.eaton.com/content/dam/eaton/products/low-voltage-power-distribution-controls-systems/motor-contols/vfd-dvdt-filter-ap043001en-application-note.pdf

Edit it says
" For a 240 V motor, the reflected wave
would be closer to 680 V, so a dV/dT filter would
not be required; however, a load reactor is always
recommended."

Which is why I earlier mentioned you likely get away with this aspect on 208-240 volts vs 480 volt application on the same (dual volt) motor. If you use same motor on 480 volts the voltage peaks put out by the drive could be well above motor insulation design. It won't fail immediately, it likely doesn't even give you a fireworks show when it fails as the ground fault detection of the drive will kick in while the fault is at a pretty low level. but it will work on deteriorating the motor insulation as time goes on. Full speed will be where you see maximum effect as it is generally going to be running at full voltage when running at full speed.

Thanks all for breaking it down, good info.
When I here 'filter' I think capacitor and resistor combo, like a 'snubber' on a relay circuit.
The load reactor appears to be just a coil.
In this particular machine the VFD to motor will be about 5-6 foot conductor run @240V.

That short of circuit length (drive to motor) another reason to not be as concerned with this issue even if you were operating at 480 volts, though still worth more consideration with motors not wound with spike resistant magnet wire in any application. Small inexpensive and easy to replace motor - maybe you just run it until it fails and replace with one with better design.

 

[ptonsparky]

Last old motor at 480 we had fail was shorted windings. Load reactor and within 30. Key word is 'old'. Still 100hp.

 

[kwired]

Last old motor at 480 we had fail was shorted windings. Load reactor and within 30. Key word is 'old'. Still 100hp.

Have a 100 HP motor at one client that is probably from late 1980's or early 90's that we put on a VFD sometime in last 5 years. ~100 feet from drive to motor. Put reactor on drive output right away on that one, no problems yet.

Part of same process in that plant is a 50 HP motor that we put on a VFD maybe 15 years ago. Didn't know so much about drives back then and issues with older motors. Had to rewind that motor about once a year after putting it on the drive. We did succeed with part of our goal of slowing that machine down as we could run at slower speed but adjust other items and still get the right consistency out of production line - the main reward was more life on some components, and probably used less power though that wasn't as obvious without monitoring that machine's power consumption.
But kind of wiped out the rewards when needing to rewind the motor about once a year. Finally convinced owners to purchase a new motor that is rated for use with VFD's as well as with a separately powered cooling fan (we run this thing down to about 30 Hz at times but at/near full load current so between poor cooling and IGBT issues the motor wasn't lasting all that long. Only thing we have done to that motor since then was to replace bearings in the cooling fan a time or two - learned the hard way to make sure to have proper overload on that tiny three phase fan motor so that it will catch bearing failure before burning out motor windings. Think it was only like 1/4 HP @ 480 three phase, tenths of amps on motor overload setting are critical on that one.

Also learned hard way on that same machine at one time that if you bypass oil pressure switch because it failed, make sure to actually replace it ASAP. it went bypassed for maybe years, then ran out of oil one time and caused lots of rework to be needed.

 

[don_resqcapt19]

We put VFDs on four 40 hp motors that were old enough that the nameplate voltage was 440 and not 460. The plant was built in the mid 60s and I expect the motors are original. The application was aeration agitators in the aeration ponds of an industrial waste water treatment plant The lead lengths from the drives to the motors are between 400' and 700'. They have load side reactors at the drives. The drive install was about 5 years ago, and no problems so far.

 

[Eddie702]

UPDATE:
So I got the ABB drive and got intouch with the motor manufacturer as they still make this motor.
And they said that since the motor is from the 70's its too old to run on a VFD and presumably I should buy a new motor.

Now my plan is not to use any VFD features, just as a phase converter, set it at 1200 RPM.
I plan to have it be triggered with an icecube relay, where the coil of the icecube is powered by the existing 120V controls.
Any thoughts/ experience on using a VFD with an old motor, like 40 years old?

Thanks all

I am sure the motor will work for a while but I would order a spare and have it on hand