# 240 Volt VFD, Long Run To Motor.



## Jerome208 (May 10, 2013)

Franklin the well pump guys make a pump/controller combo that does exactly what you are describing out of the box. They vary motor speed based on demand and use a very small accumulator rather than a pressure tank.

The selling point is no water pressure fluctuations but it also is a polyphase motor.


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## varmit (Apr 19, 2009)

Yes, you would need a load reactor. Also, don't undersize the wire on a run this long. I believe that your plan is the way to do this, as a three phase motor normally has a longer life in pump applications.


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## triden (Jun 13, 2012)

We almost always use a VFD as a phase converter when we only have single phase power for pumping applications - good choice IMO. At 240v, it's a bit of an experiment as to how long the motor will last without a reactor (it may last forever), but an 800' pump is not one you will want to pull very often. I would install a load reactor without question on an 800' cable because for the price it's cheap insurance. If it were 100 feet, I would sleep really well at night without a load reactor, but not for this one.

Now on the same note, there becomes a a time when increasing the length of cable will actually reduce insulation stress on the motor. At a certain length (not sure of the factor off hand), the incoming voltage and the reflected voltage combine to create a lower overall dv/dt in the cable thus lowering the insulation stress. I just thought I would throw in that tidbit even if it doesn't help much in determining if it applies to your situation.


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## JRaef (Mar 23, 2009)

In general I don't use load reactors on 230V motors because most of them are 230/460V, so the magnet wire will be selected based on the 460V and the insulation value will be higher than what standing wave spikes can get to on a 230V VFD output. But on submersibles, the motors are not commercial off the shelf designs, so it's more likely that this might not be the case. Also, at that distance I would also be concerned (maybe even more so) about possible bearing EDM damage. I would use a DV/DT output filter for that reason alone, with the winding insulation protection as a side benefit.


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## micromind (Aug 11, 2007)

Thanks, guys. I kinda figured I'd need to do something, considering the length. But I have worked with very few 240 VFDs, and those were short runs.


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## JRaef (Mar 23, 2009)

TCI makes a good DV/DT filter, not very expensive for that size, and a LOT cheaper than having to pull that pump. You should be able to get one from GMI in Reno.


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## micromind (Aug 11, 2007)

JRaef said:


> TCI makes a good DV/DT filter, not very expensive for that size, and a LOT cheaper than having to pull that pump. You should be able to get one from GMI in Reno.


Thanks!

GMI is the Allen Bradley dealer, I use a TON of A/B stuff so if I decide to go this route, I'll ask them about it.


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## A Little Short (Nov 11, 2010)

I'm interested in learning VFDs but know very little about them. I won't ask any questions here as I don't even know what to ask!:no:

I do have a couple of questions though concerning this thread.

What is a load reactor?

What is DV/DT?


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## oliquir (Jan 13, 2011)

you may have to readjust the V/F curve and boost voltage a little to compensate for voltage drop also


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## JRaef (Mar 23, 2009)

A Little Short said:


> I'm interested in learning VFDs but know very little about them. I won't ask any questions here as I don't even know what to ask!:no:
> 
> I do have a couple of questions though concerning this thread.
> 
> ...


A reactor is just a simplistic inductor, copper wires wrapped around an iron core. Just like half of a transformer, in that there is only the one winding. It doesn't change the voltage, it just adds inductance, which changes the impedance of the circuit. Line or Load just denotes which side of the drive you wire it to, but it also affects the size. A load reactor has to be a little larger because it has to pass all of the current going to the motor, active and reactive. But on the line side, the VFD corrects the power factor, so the input current is a little lower and the reactor can be a little smaller and cheaper. 

DV/DT (actually dV/dt, but all caps is used for product names) is shorthand for delta Voltage over delta time. Delta in math terms means "change" or "difference", so it means the change in voltage divided by the change in time. In drive terms, it's referring to the rapid rise time of the tiny DC pulses that come out of the drive transistors that make the entire technology work. So the higher the dV/dt, the faster the rise time of the leading edge of each pulse. So in older drives, that used to be someting like 5V/microsecond, but in the latest generation of high speed transistors being used now, it's around 50V/microsecond. 

That fast rise time starts to make things like conductors separated by insulation fit the definition of a capacitor better and better, so the longer the cables, the more capacitance they exhibit. The voltage in those "capacitors" causes several problems in motor circuits run by VFDs, and the longer the cables get, the worse the problems become because it increases that voltage potential. It can get to where the theoretical voltage can pike to up to over 3x the applied voltage. On a 480V drive, the DC bus voltage is at least 635V, so it can get to over 2,000V spikes and if the motor insulation is only rated for 1200V as it was for years, the spikes eventually burn through. So filtering them becomes more important the longer the cables get. Newer "inverter duty" motors use higher insulation voltages, but there are other issues to contend with as well, so if you want your motor to last longer, it's best to invest in filtering if you have really long cable runs.


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## NC Plc (Mar 24, 2014)

Man I learn so much from threads like these.


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## Hybwolf (Jul 31, 2011)

JRaef,

Under what circumstances would a dV/dT filter be used instead of a load reactor?

Tony


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## JRaef (Mar 23, 2009)

I only recommend load reactors in 3 circumstances: 1) when the issue is primarily one of protecting the VFD from faults on the motor cable, such as on mobile equipment where the motor cable is subject to getting damaged. 2) when there is a very short run, as in under 25ft, but it's to a really old motor that is difficult to replace. 3) when you have multiple motors being run by one VFD, i.e. a 10HP VFD running 5 x 2HP motors. The reason for that is because when you have 5 motors, you have 5x the cable length (in total circuit length, not physical distance from the VFD), and 5x the chances of a circuit issue, such as a ground fault.

Over 25' and under 1000', use a dV/dt filter, over 1000' use a Sine Wave filter, which is a step up on the filtering technology over a dV/dt filter, but the cost is a lot more.


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