# VFD help



## Bewildered (Mar 19, 2012)

Have had 2 Vfds on the same piece of equipment go bad by an apparent
line to line short circuit. It destroyed the line contactor, tripped the motor
C.B., the feed C.B., and the main C.B. feeding the panel.
Motor was meggered line to line, and line to ground with no bad readings.
It is now running fine in bypass mode.

Vfd #1 was a Saftronics FP5/GP5, #2 was a Westinghouse TECO MA7200
Motor is a 2HP, at 480 volts.

Any suggestions?


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## Dennis Alwon (May 9, 2009)

bump


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## nolabama (Oct 3, 2007)

What kind of equipment?


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## MDShunk (Jan 7, 2007)

I wouldn't normally guess it on a 2-horse application, but it sure sounds like you need a line reactor on that setup. 

Does this load cycle frequently? Do you stop the load by sending the stop command to the VFD, or opening the line side contactor?


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## John Valdes (May 17, 2007)

Bewildered said:


> Have had 2 Vfds on the same piece of equipment go bad by an apparent
> line to line short circuit. It destroyed the line contactor, tripped the motor
> C.B., the feed C.B., and the main C.B. feeding the panel.
> Motor was meggered line to line, and line to ground with no bad readings.
> ...


Lets get this straight. You have a line side *contactor* fried and you are now running in bypass mode? Or did the *"line reactor" *fry?
Maybe the contactor failed? Remove the bad contactor and take it apart and see what happened. What do you actually have? Reactor or contactor?
If it is a contactor, why? Safety E-Stop?


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## JRaef (Mar 23, 2009)

As John said, you need to describe the purpose and function of the line contactor (if that's what it is). If the system is turning the drive on and off with the line contactor every time, that's a bad design. It stresses the capacitor charging resistor inside of the drive, which if it burns out leads to rapid failure of the other components in the drive. If the input diodes short, it's a bolted fault, hence the breakers tripping. The fact that it happened on a second drive from a different mfr. points to that or some similar problem.


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## acro (May 3, 2011)

Have you looked at the connections at the motor?

We have heavily damaged a couple of 480amp soft starts from phase-phase shorts caused by long term vibration at the peckerhead.

Did you ever find the source of the short? Didn't sound like you did.


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## JRaef (Mar 23, 2009)

acro said:


> Have you looked at the connections at the motor?
> 
> We have heavily damaged a couple of 480amp soft starts from phase-phase shorts caused by long term vibration at the peckerhead.
> 
> Did you ever find the source of the short? Didn't sound like you did.


That's entirely possible on Soft Starters but for the most part any fault on the load side of a VFD will be picked up by the VFD protection circuit and it will trip much faster than anything up stream will be able to react to. Most UL listed VFDs will be listed as the Short Circuit Protective Device for the motor side, because for all intents and purposes, the output of a VFD is a "separate source" as far as protection is concerned. A tripped upstream protective device pretty much indicates the issue lies on the line side of the VFD.


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## Bewildered (Mar 19, 2012)

JRaef said:


> As John said, you need to describe the purpose and function of the line contactor (if that's what it is). If the system is turning the drive on and off with the line contactor every time, that's a bad design. It stresses the capacitor charging resistor inside of the drive, which if it burns out leads to rapid failure of the other components in the drive. If the input diodes short, it's a bolted fault, hence the breakers tripping. The fact that it happened on a second drive from a different mfr. points to that or some similar problem.


Ok, bad description. The contactor is the input to the VFD. There is a DC reactor in the cabinet. This unit is an exhaust fan that runs 24/7, except
twice a year when it is shut down for PM and cleaning. When shutting down I give a stop command at the VFD keypad, wait 'til the unit shows stop, turn the control switches off, and then turn off power. The drive
output is controlled by the BMS. The 2nd VFD was only in service about 
1 month.


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## John Valdes (May 17, 2007)

Bewildered said:


> Ok, bad description. The contactor is the input to the VFD. There is a DC reactor in the cabinet. This unit is an exhaust fan that runs 24/7, except
> twice a year when it is shut down for PM and cleaning. When shutting down I give a stop command at the VFD keypad, wait 'til the unit shows stop, turn the control switches off, and then turn off power. The drive
> output is controlled by the BMS. The 2nd VFD was only in service about
> 1 month.


Whats a DC reactor? What is a BMS?
Do you have regeneration capability on this drive. Meaning is it possible you are regenerating to much voltage back to the drive during ramp down?
This could increase the bus voltage and cause it to trip. 
Is the drive in "variable torque" mode? Fans and pumps are usually easy on drives if you take care of the regen power.

Also, do you ever start the drive when the motor is turning the opposite direction? Meaning, if the fan is turning backwards because of draft, the current required to bring the fan to a complete stop and then to the set speed you have selected becomes very difficult?
Does your drive have a "on fly" start feature? Jraef will be along I am certain and can address anything I have missed.

One more thing. What is the contactor for? I do not ever advise anyone to put a contactor in front of the control.


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## JRaef (Mar 23, 2009)

John Valdes said:


> Whats a DC reactor? What is a BMS?
> Do you have regeneration capability on this drive. Meaning is it possible you are regenerating to much voltage back to the drive during ramp down?
> This could increase the bus voltage and cause it to trip.
> Is the drive in "variable torque" mode? Fans and pumps are usually easy on drives if you take care of the regen power.
> ...


I would assume he meant a DC link choke, looks exactly like a reactor Some (mostly Asian) drives don't come with them but you can add th in the field after the fact. This sounds like one if those. 

BMS would be a Building Managemt System, it's an HVAC term for the control system that is telling the VFD when to come on and off and what speed to run. 

I think the regen issue might make the drive trip on Over Voltage, but should not cause the the front end of the drive to fail or fuses to clear etc. 

I'm still not clear on what the line contactor is doing though if the drive runs 24/7/365 except for PM shutdowns. I still think that may be your culprit if it isn't something else like a ground fault on the line side. Could the BMS be inadvertently opening and closing that contactor when nobody is looking? 

But hmmm... a ground fault on the conductors of an external DC Link Choke? Very possibly could be another suspect in this crime. Its going to be right off of the DC bus so if there is a fault in the conductors, it would damage the diode front end, which as I said would then clear the fuses etc. If you leftward the motor leads, it would not be seeing that. But DO NOT legged anything that is connected to the VFD. Disconnect from it and then legged the conductors.


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## nolabama (Oct 3, 2007)

Legged?


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## JRaef (Mar 23, 2009)

JRaef said:


> I would assume he meant a DC link choke, looks exactly like a reactor Some (mostly Asian) drives don't come with them but you can add th in the field after the fact. This sounds like one if those.
> 
> BMS would be a Building Managemt System, it's an HVAC term for the control system that is telling the VFD when to come on and off and what speed to run.
> 
> ...


"leftward" and "legged" in the above are Apple's interpretations of the word "megger" for some reason.


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## nolabama (Oct 3, 2007)

I turned all that stuff off. I thought it was megger but had to ask.


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## JRaef (Mar 23, 2009)

nolabama said:


> I turned all that stuff off. I thought it was megger but had to ask.


I hate the fact that I can't add words to Apple's dictionary. It auto corrects contactor to contractor all the time too. Pisses me off. 

Someone is probably going to tell me now that I could have changed something somewhere to make it work, but damnit, that means I would have to RTFM. No can do... It affects my manhood.


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## JRaef (Mar 23, 2009)

nolabama said:


> I turned all that stuff off. I thought it was megger but had to ask.


Tried to respond to your PM on the prox device, you have exceeded your limit and cannot receive any more messages until you clear some space. Lol.


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## nolabama (Oct 3, 2007)

Will fix stat.


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## [email protected] (Apr 1, 2012)

*Ara calibasi*

I have 4 4 motors wired on one vfd power wiring on the same conduit this will cause harmonic problem?


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## JRaef (Mar 23, 2009)

[email protected] said:


> I have 4 4 motors wired on one vfd power wiring on the same conduit this will cause harmonic problem?


You should start a new thread on this question.


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## lukejenson (Sep 14, 2009)

I use reactors from Trans-Coil, especially their KDR series.

http://www.clrwtr.com/TCI-KDR-Line-Reactor.htm


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## greenman (Apr 20, 2012)

Are you using a solid stat contactor?


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## oliquir (Jan 13, 2011)

seems to me that it was not a s/c but a severe overvoltage thats makes the vfds, fuses, contactor broke.


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## T-DAWG (Jun 30, 2021)

What amp/voltage readings are you getting throughout the setup and include pictures of the wiring/VFD.


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## JRaef (Mar 23, 2009)

T-DAWG said:


> What amp/voltage readings are you getting throughout the setup and include pictures of the wiring/VFD.


9 years later, he probably no longer cares.


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## T-DAWG (Jun 30, 2021)

JRaef said:


> 9 years later, he probably no longer cares.


Didn't even see that.


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## JRaef (Mar 23, 2009)

T-DAWG said:


> Didn't even see that.


Yeah, we all do it...


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## Wirenuting (Sep 12, 2010)

JRaef said:


> 9 years later, he probably no longer cares.


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