# BenshawVFD repetitive failure



## Dennis Alwon (May 9, 2009)

Welcome


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## gesparky221 (Nov 30, 2007)

Do you have line reactors or filters on these drives? I would also check the wiring to the motor with a megger after it is disconnected from the drive. VFD's can damage the insulation on field wiring. I have also had a couple motors cause problems like this. We only use the inverter rated motors any more. I have checked the field wiring with a ohmmeter and they will test ok. But with a megger they fail.


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## JRaef (Mar 23, 2009)

gesparky221 said:


> Do you have line reactors or filters on these drives? I would also check the wiring to the motor with a megger after it is disconnected from the drive. VFD's can damage the insulation on field wiring. I have also had a couple motors cause problems like this. We only use the inverter rated motors any more. I have checked the field wiring with a ohmmeter and they will test ok. But with a megger they fail.


I agree, one common mistake is testing cables at too low of a level when using drives. Even if people megger the leads, they often megger them at 500V because that's the megger they have available for normal power applications but on a 480V drive, the PWM pulse voltage is almost 700VDC peak so the insulation failures may not show up at 500VDC. You need to use a 1000V megger. By the way ALWAYS disconnect the VFD from the motor leads before using a megger.

If you only used a multimeter to check the cables, that is essentially meaningless. You checked them for 9VDC applications.


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## [email protected] (Mar 28, 2012)

We have both line and load reactors, identical sources (600VAC)- same buss. Identical drives and motors, four failures on one setup only, no problems with other one. Power quality was found to contain some harmonics but Benshaw dismissed this as problem. I been looking for real out there solutions,spidie sense pointing me at line impedance/harmonic issues possible reaching "perfect storm" potential with one system and not the other or maybe altering reactors function. ??? Hopefully one of you highly trained/experienced gurus can give me some input. Thanks:blink:


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## John Valdes (May 17, 2007)

What failed in the VFD? Input or output section? Blowing up can happen on either end. Same buss? You share a buss? What do you mean "same buss"?
A short circuit in a jbox should have resulted in a trip, not a blown up drive. Please be more technical if you want a technical answer. Things blowing up is a lot different than lets say "the input bridge was destroyed".
I like Benshaw and they build stout controls. Maybe you can expand on the "refitting" the cooling tower with specifics. What did you do exactly.
Drives are built with so much protection today, its not common to blow one up.


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## JRaef (Mar 23, 2009)

John Valdes said:


> What failed in the VFD? Input or output section? Blowing up can happen on either end. Same buss? You share a buss? What do you mean "same buss"?
> A short circuit in a jbox should have resulted in a trip, not a blown up drive. Please be more technical if you want a technical answer. Things blowing up is a lot different than lets say "the input bridge was destroyed".
> I like Benshaw and they build stout controls. Maybe you can expand on the "refitting" the cooling tower with specifics. What did you do exactly.
> Drives are built with so much protection today, its not common to blow one up.


Although they don't actually build their VFDs, they are LS (the new name for LG out of Korea).

Still, John's point is valid, VFDs are all now pretty good and if you get multiple failures in the same installation, that moves the needle on the Possibility-o-Meter firmly to the side of "Installation Problem". A description of exactly WHAT failed in the drive would help to point towards a problem on the input or output side.

Another thought that came up for you [email protected], you didn't by chance run the outputs of these drives in the same conduit did you? That's another big no-no unless you use shielded VFD output cable.


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## gottspeed (Mar 8, 2010)

I was wondering what this new fancy VFD teck cable was for but I'm beginning to see that mutual induction can be a problem hence the need for reactors and the special cable.

I wonder if the ground fault that you had damaged some insulation somewhere. A multimeter won't show a fault as well as the behavior of damaged insulation with peak voltage on it.


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## John Valdes (May 17, 2007)

gottspeed said:


> I was wondering what this new fancy VFD teck cable was for but I'm beginning to see that mutual induction can be a problem hence the need for reactors and the special cable.
> 
> I wonder if the ground fault that you had damaged some insulation somewhere. A multimeter won't show a fault as well as the behavior of damaged insulation with peak voltage on it.


I left the actual hands on working in this discipline before the cables got so much popularity. But, I am a big believer in input, line side filtering (reactors). Cheap insurance and so well proven, most manufacturers do recommend reactors when purchasing drives. Line reactors not load reactors. They will even discount the line reactors on the initial purchase. At least they did last I checked.
The cables. I never used them before. But they have their place. For me THHN/THWN and a separate conduit or raceway to the motor was sufficient. I am certain it still is.
I always thought the cable was way to expensive, since my separation method worked so well, I never had to use them.
Not to say I would not use them. Customers get what they want, even if they don't need it.


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## JRaef (Mar 23, 2009)

John Valdes said:


> ...The cables. I never used them before. But they have their place. For me THHN/THWN and a separate conduit or raceway to the motor was sufficient. I am certain it still is.
> I always thought the cable was way to expensive, since my separation method worked so well, I never had to use them.
> Not to say I would not use them. Customers get what they want, even if they don't need it.


You are still right, separate conduits and THHN/THWN are fine. You really only need the special shielded VFD cable when running in cable tray or common raceways, which is what they do in Europe and other countries. They don't use separate conduits unless they have a gun to their heads about it. All in all, probably a wash in terms of installed cost, but unfortunately I see a lot of Consultants spec out the VFD cables INSIDE of separate conduits because nobody talks to them about this, which is overkill and therefore much more expensive and then leads to people thinking VFDs are too expensive to use. Sad but true.


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