# Vfd



## Ninjazx916r (Apr 1, 2011)

So the VFD is more than 50 ft from the motor and in the past, it has cause some problems. So this time when we install new ones we added a filter. We didn't install it yet because the instructions said install it within 10 feet from the drive. This will still make the filter more than 50ft away from the motor. Will the filter help even if its that far away?


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## sparky970 (Mar 19, 2008)

If it's a motor terminator/output filter, it should be installed near the motor.


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## glen1971 (Oct 10, 2012)

What kind of filter are you adding?

I've never installed a load reactor near the motor.. They are usually right beside, adjacent to, or in the same cabinet as the VFD... Distance to the motor has never caused an issue, and has been in the 100's of feet..


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## DriveGuru (Jul 29, 2012)

Is it a DV/DT filter, or just a line reactor, you want a DV/DT filter, this has an added R/C network to knock down the standing wave. And yes close to the drive, otherwise it won't be effective protecting the drive and motor. The resistance of the added lead length putting it at the motor will render it less effective.


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## John Valdes (May 17, 2007)

sparky970 said:


> If it's a motor terminator/output filter, it should be installed near the motor.


Nope. As close to the drive as possible.
One time I had a customer buy 10 drives, with motors and line and load reactors.
Over the weekend they brought in a crew to do all the work.
Some how they got a hold of the drive manufacturer and were told to mount the reactors at the motors.
So they went and got 10 enclosures and installed the reactors near each motor.
On Monday morning I showed up to see how they were progressing. I had them removing the load reactors and enclosures and had them installing them in the large cabinet directly adjacent to the drive cabinet..

The project manager was very upset because he got this wrong information from the actual manufacturer. I told him to call me next time.
I got the manufacturer to pay for the extra time, the enclosures and any other cost directly related to the bad information.

They were able to locate the rep who gave the bad info as he was on call that weekend and admitted he told them to mount the reactors near the motors.


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## JRaef (Mar 23, 2009)

So as you can see, the term "filter" is a little too vague to be able to respond to with any certainty. But if it is a dV/dt filter or a "sine wave" filter, it's purpose is to reduce / eliminate the capacitive coupling that takes place inside on the motor leads caused by the high speed at which the transistor pulses are taking place, creating what is called a "reflected wave" phenomenon that results in waves of high voltage that eventually spike to a level that break down the motor or wiring insulation.

Those filters will have two main components to them, a load reactor to add an inductive time constant to the circuit that slows down the rise time of the leading edges of the pulses, which reduces the primary cause in the first place, and a high voltage trap for anything that gets through and reflects back. The reflection is a key component of the problem, in that the "wave" of higher voltage created by the cable capacitance travels down the wires until it hits an impedance change, such as the motor terminations, then goes back to the other end impedance change, the drive terminations, or in this case the reactor terminals, and bounces back and forth, building up on itself until the voltage level exceeds the winding insulation and burns through. So even with the load reactor, some of the cable capacitance still happens but when it bounces back from the motor terminals, the trap absorbs it and burns it off in resistors.

In this action packed scenario, if you put the dV/dt filter too far away from the drive, you get the phenomenon happening between the drive and the filter, plus again between the filter and the motor. But the filter wasn't really designed to fight a war on two fronts, so you can overheat the resistive traps, lose them, then you don't have them any more, so the problem moves to the next weak link and the filter ends up being a waste of money. You could put the filter next to the motor too, but the reflected wave phenomenon will then take place in the motor leads instead. So the best place to put them is as close to the drive as possible.

There are also trap-only devices that mount near the motor. They do not help prevent the problem because they don't have the reactor to slow down the transistor pulse rise time, but they trap those resulting high voltage reflected waves before they can get to the motor insulation. They can leave the motor lead wires exposed to risk however if the length is too long.

At 50' drive-to-motor, a dV/dt filter might be a little over kill, but can't hurt. A load reactor alone or a trap filter alone would likely be fine for that. But ask your drive mfr what they recommend, they know their drive better (or should).


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## DriveGuru (Jul 29, 2012)

JRaef said:


> So as you can see, the term "filter" is a little too vague to be able to respond to with any certainty. But if it is a dV/dt filter or a "sine wave" filter, it's purpose is to reduce / eliminate the capacitive coupling that takes place inside on the motor leads caused by the high speed at which the transistor pulses are taking place, creating what is called a "reflected wave" phenomenon that results in waves of high voltage that eventually spike to a level that break down the motor or wiring insulation. Those filters will have two main components to them, a load reactor to add an inductive time constant to the circuit that slows down the rise time of the leading edges of the pulses, which reduces the primary cause in the first place, and a high voltage trap for anything that gets through and reflects back. The reflection is a key component of the problem, in that the "wave" of higher voltage created by the cable capacitance travels down the wires until it hits an impedance change, such as the motor terminations, then goes back to the other end impedance change, the drive terminations, or in this case the reactor terminals, and bounces back and forth, building up on itself until the voltage level exceeds the winding insulation and burns through. So even with the load reactor, some of the cable capacitance still happens but when it bounces back from the motor terminals, the trap absorbs it and burns it off in resistors. In this action packed scenario, if you put the dV/dt filter too far away from the drive, you get the phenomenon happening between the drive and the filter, plus again between the filter and the motor. But the filter wasn't really designed to fight a war on two fronts, so you can overheat the resistive traps, lose them, then you don't have them any more, so the problem moves to the next weak link and the filter ends up being a waste of money. You could put the filter next to the motor too, but the reflected wave phenomenon will then take place in the motor leads instead. So the best place to put them is as close to the drive as possible. There are also trap-only devices that mount near the motor. They do not help prevent the problem because they don't have the reactor to slow down the transistor pulse rise time, but they trap those resulting high voltage reflected waves before they can get to the motor insulation. They can leave the motor lead wires exposed to risk however if the length is too long. At 50' drive-to-motor, a dV/dt filter might be a little over kill, but can't hurt. A load reactor alone or a trap filter alone would likely be fine for that. But ask your drive mfr what they recommend, they know their drive better (or should).


Hmmm...from your explanation of reflected wave, I believe I have been misunderstanding the filters a little bit. I was thinking the rc network was what they were using to slow the rise time of the leading edge of the pulse. I guess I never really considered the capacitance of the motor leads. So if I understand you correctly, the load reactor limiting the current lengthens the rise time of the pulse, and the rc network is like a snubber circuit so to speak for dissipating the actual reflected wave. Thank you for clearing that up for me.


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## JRaef (Mar 23, 2009)

DriveGuru said:


> Hmmm...from your explanation of reflected wave, I believe I have been misunderstanding the filters a little bit. I was thinking the rc network was what they were using to slow the rise time of the leading edge of the pulse. I guess I never really considered the capacitance of the motor leads. So if I understand you correctly, the load reactor limiting the current lengthens the rise time of the pulse, and the rc network is like a snubber circuit so to speak for dissipating the actual reflected wave. Thank you for clearing that up for me.


Yes, exactly, if you look at them, it's an RC snubber circuit (I just said resistor to be less confusing). The heart of the problem begins with the capacitance in the cables, in fact a separate issue when motor leads get REALLY long begins to be that the capacitance charging current of that circuit can exceed the dI/dt (change in current rate) of the transistors in the drive and cause damage to them too. How the transistors are fired is a way a few mfrs have discovered for mitigating some of this (but if I told you how, I'd have to kill you), that's why you can sometimes see manufacturers list longer distances that one can go from drive to motor. But that does not necessarily solve the reflected wave issue. So the "motor terminator" devices are just the RC Snubbers that you put at the motor end, and combined with the transistor firing technique can be fine without the reactor. But I like having the reactor for the inductance anyway, because it also slows the rise rate of faults on the motor side to give the VFD time to react and shut itself off, avoiding collateral damage. it's cheap insurance. So I always tell people that if there is any appreciable distance from drive to motor, put in at LEAST a load reactor, then upgrade to a filter only if necessary.


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## DriveGuru (Jul 29, 2012)

JRaef said:


> Yes, exactly, if you look at them, it's an RC snubber circuit (I just said resistor to be less confusion). The heart of the problem begins with the capacitance in the cables, in fact a separate issue when motor leads get REALLY long begins to be that the capacitance charging current of that circuit can exceed the dI/dt (change in current rate) of the transistors in the drive and cause damage to them too. How the transistors are fired is a way a few mfrs have discovered as a way of mitigating some of this (but if I told you how, I'd have to kill you), that's why you can sometimes see manufacturers list longer distances that one can go from drive to motor. But that does not necessarily solve the reflected wave issue. So the "motor terminator" devices are just the RC Snubbers that you put at the motor end, and combined with the transistor firing technique can be fine without the reactor. But I like having the reactor for the inductance anyway, because it also slows the rise rate of faults on the motor side to give the VFD time to react and shut itself off, avoiding collateral damage. it's cheap insurance. So I always tell people that if there is any appreciable distance from drive to motor, put in at LEAST a load reactor, then upgrade to a filter only if necessary.


I understand...sounds like a little bit of smoke and mirrors on the transistor firing. The dark side likes using the term"just in time firing", I see that more as reducing the repetition of hits rather than mitigating them but whatever sells I guess,lol


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## oliquir (Jan 13, 2011)

usually you don't need load reactor unless you have more than 2-300 foot or you have a very cheap vfd


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## MDShunk (Jan 7, 2007)

All this talk about "filters".....

What I really want to know is what for brand of cheap crap drives start to wig out when the load is just over 50 feet away? I'd probably consider buying a good drive first. :laughing: With the load side ckt in VFD cable, I don't really start to think about load reactors until 150 feet or so with the brands I normally work with.


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## DriveGuru (Jul 29, 2012)

MDShunk said:


> All this talk about "filters"..... What I really want to know is what for brand of cheap crap drives start to wig out when the load is just over 50 feet away? I'd probably consider buying a good drive first. :laughing: With the load side ckt in VFD cable, I don't really start to think about load reactors until 150 feet or so with the brands I normally work with.


If you are buying either one of the top 2 drive manufacturers, you're using the drives JR and I were discussing. But in really this will apply to ANY drive that uses a fast switching device such as an IGBT. Are you using old darlington transistor drives or maybe scr commutating? Lol 

Unfortunately most people don't use "vfd" cable such as O-FLEX. I keep getting told by contractors that THHN meets code, yes it does...but try to convince them to actually READ any mfg's installation manual. Then when they have noise issues with other equipment I'm the bad guy. 

We are also not really talking about the drive having issues here, the guy we were trying to help keeps losing motors but you can rest assured what we were discussing happens with EVERY drive.


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## Ninjazx916r (Apr 1, 2011)

So we ended up installing as close to the VFD as possible. Inside it just look like a tiny transformer with a circuit board mount to the side of the enclosure. Then now I was told that the line side has to be in a separate conduit than the load side.


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## DriveGuru (Jul 29, 2012)

Ninjazx916r said:


> So we ended up installing as close to the VFD as possible. Inside it just look like a tiny transformer with a circuit board mount to the side of the enclosure. Then now I was told that the line side has to be in a separate conduit than the load side.


Yes sir it does, mostly to prevent the vfd from messing with other equipment, possible drive issues but most of the time not. Control wires should be in a separate conduit as well. This is standard in just about any drive installation manual. What type of drives are you using?


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## Ninjazx916r (Apr 1, 2011)

The VFD brand has a ABB on the cover.


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## DriveGuru (Jul 29, 2012)

Ninjazx916r said:


> The VFD brand has a ABB on the cover.


Those are kind of a specialty of mine. Input and output sharing by the book is prohibited, but I see it done allot unfortunately. As far as affecting the drive, it probably won't, it can mess with the flying start feature, and possibly auto-tune, but more than likely just that. Multiple drive output leads in the same conduit can cause nuisance trips. It can possibly interfere with other equipments sensors and communication(output leads inducing noise on the incoming)


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