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Old 03-13-2019, 06:01 PM   #1
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Default Motor short causing VFD Failure

At work, we have conveyors to move chicken crates. Due to the constant sanitation every night the motors driving these conveyors only last around 6 months. The motors usually short to ground. We replace the motors but also find that the VFD feeding them is also burnt out. The motors have a FLA of 2.1 amps so we have them hooked up to a Leeson 174491.00 (2 HP, 600 volts, output 3 amps). We have no line or load reactors installed and the VFD is protected on the line side by an IEC style motor protector (short circuit and overload protection built into one).

My thinking is the motor protector is not fast enough to trip to protect the drives. I am thinking about changing the motor protectors to fast acting fuses as listed in the VFD manual and adding a line side reactor. What do you guys find is the best way to protect these small VFD's?

Last edited by lynes.nathan; 03-13-2019 at 06:03 PM.
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Old 03-13-2019, 06:24 PM   #2
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Your current limit should protect the drive when a motor goes bad.. Not sure if that's your problem. what's parameter 25 and 26 set to? I to work at a wash down facility and our lesson motors go bad, but our GS2 and Poweflex drives do what they're suppose to when an over current or ground fault occurs.

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Old 03-13-2019, 06:41 PM   #3
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Parameter 25 is at default (180%). Parameter 26 is the motor FLA divided by the VFD current rating, so 2.1 amps / 3 amps= 0.7 so its set to 70%
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Old 03-13-2019, 10:30 PM   #4
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Ever think about GS2 drive? gs2's are cheap and I can confirm they a good at handling ground and Phase-Phase faults from water.

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Old 03-14-2019, 02:08 PM   #5
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Ground faults on the output side are not going to be protected by anything on the input side, the VFD should be doing that internally.
  1. Check the grounding. You MUST have the ground wire from the motor run to the Ground terminal in the VFD, not to anything else first. The VFD NEEDS that reference point for the Fault protection to trip. If someone thought that the ground for the motor can be accomplished via conduit, that's the first mistake. Pull the ground wire. If there is a dedicated ground wire and it is terminated ON the VFD ground terminal, that's good.
  2. Install a load reactor. The rise time of a grounded fault on the load side of a VFD can be too fast for the VFD protection systems to react to it. Adding a load reactor will slow down that rise time and allow the VFD to protect itself.
  3. Get better motors. People make wash-down duty motors for this type of application. 6 months life is a ridiculous thing to live with.
  4. You might want to consider a better VFD. First off, pursuant to #1, that particular drive is designed to be as cheap as humanly possible, so it does not even HAVE a separate Ground Fault protection scheme, it relies on basic Current Trip functionality. That MAY work (if you have a load reactor), but drives that actually use a Residual Current Detection method do much better at detecting GF issues before they can cause damage.

    4b) 600V rated VFDs are expensive because the transistors that can handle the peak voltages seen in 600V systems are rare, i.e. less than 1% of the production of the transistors will pass. Leeson just brand-labels these drives from a company that was called AC Tech (now Lenze). Unfortunately when AC Tech originally designed those 600V versions of their drives, they chose to use standard 480V rated power modules and take a chance that they would survive at 600V, assuming that if not, it will fail immediately and they replace them under warranty, which would cost them less vs designing, manufacturing, maintaining inventory and supporting a totally separate product line. This strategy backfires on the end users.
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Old 03-25-2019, 11:46 AM   #6
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Sorry for my late response.

If nothing on the input side of the drive will protect the drive from ground faults then what's the idea of semiconductor fuses? I thought they were designed to protect the drives components under short circuit conditions.

1. Check the grounding I took a look inside the panel and noticed that the drive has no bond wire attached to it. We have a 14 AWG bond wire from the motor to the panel but the drive is relying on the mounted screws for the bonding. I am going to change that so we have a direct bond wire.

2.Install a load reactor This is something I definitely want to add. I have no more room inside the panel but plan to add a small panel next to it.

3.Get better motors Honestly 6 months for a motor to last in this type of environment is pretty typical. We have washdown stainless steel motors inside the clean area of the plant that last around this long. The amazing thing is we have some 15+ plus year old non washdown motors exposed to the same water and chemicals that are still going. Built in the USA.

4.Get a better VFD That is something I want to look into but right now we have a lot of stock of these Leeson VFD's.
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Old 03-25-2019, 01:50 PM   #7
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Are they invertor duty motors?
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Old 03-25-2019, 05:50 PM   #8
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Quote:
Originally Posted by lynes.nathan View Post
Sorry for my late response.

If nothing on the input side of the drive will protect the drive from ground faults then what's the idea of semiconductor fuses? I thought they were designed to protect the drives components under short circuit conditions.
I make this argument all the time for small (30HP and less) drives. The ONLY thing that a semiconductor fuse can do for you is to limit the "collateral damage" of a VFD going bad. The output is essentially isolated from the input by virtue of the AC-to-DC-to-AC conversion process. So the ONLY thing that will make those expensive fuses clear is if the rectifier blows up, in which case you haven't "protected" anything, because nothing in that drive is repairable anyway. So the only people who benefit from the expensive semiconductor fuses are the people who make and sell semiconductor fuses... in other words, they are a waste of money; use standard fuses.




Quote:
... I took a look inside the panel and noticed that the drive has no bond wire attached to it. We have a 14 AWG bond wire from the motor to the panel but the drive is relying on the mounted screws for the bonding. I am going to change that so we have a direct bond wire.
You should NEVER rely upon the mounting screws as the ground for the VFD. You also MUST run a ground wire from the motor and terminate it DIRECTLY to one of the VFD grounding screws.


Quote:
This is something I definitely want to add. I have no more room inside the panel but plan to add a small panel next to it.
Totally acceptable way to do it. just make sure that ground wire from the motor goes past the reactor straight to the VFD.


Quote:
Honestly 6 months for a motor to last in this type of environment is pretty typical. We have washdown stainless steel motors inside the clean area of the plant that last around this long. The amazing thing is we have some 15+ plus year old non washdown motors exposed to the same water and chemicals that are still going. Built in the USA.
Sterling motors makes one of the best wash-down type motors on the market. Not cheap, but certainly cheaper than replacing them every 6 months. I've used them in a plant that MADE hydrochloric acid, they laster for years and years.

https://www.sterlingelectric.com/


Quote:
That is something I want to look into but right now we have a lot of stock of these Leeson VFD's.
LOL, I get it, you need lots of them if you have to keep replacing them...
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Old 03-25-2019, 06:54 PM   #9
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I use sterlings and they are decent for sure. Only complaint is the peckerheads come loose and fail from water. (Regularly) I suspect vibration but it's hard to tell. For all I know people use the pecker head as a step stool.

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Old 03-25-2019, 07:02 PM   #10
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Quote:
Originally Posted by just the cowboy View Post
Are they invertor duty motors?
Yes they are all invertor rated motors. Some of them that fail are connected to contactors not VFD's
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Old 03-25-2019, 07:15 PM   #11
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JRaef, which VFD do you recommend as a replacement for the Leeson's?

We actually do have some of those Sterling motors and come to think of it they do last a long time.
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Old 03-25-2019, 07:20 PM   #12
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I work for a VFD mfr, so it wouldn't be ethical for me to recommend my own products, so I'll defer to others...
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Old 03-25-2019, 09:38 PM   #13
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Quote:
Originally Posted by lynes.nathan View Post
JRaef, which VFD do you recommend as a replacement for the Leeson's?

We actually do have some of those Sterling motors and come to think of it they do last a long time.
I've had very good luck with Allen Bradley.

I also like Baldor but they are now ABB and I don't know if they're the same or not.
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Old 03-28-2019, 12:46 PM   #14
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I've had very good luck with Allen Bradley.

I also like Baldor but they are now ABB and I don't know if they're the same or not.

I also have had good experiences with Allen-Bradley drives, once I learned how to easily navigate the wizards and parameters. Most difficulties I've had with them were due to my own inexperience. Once they're set up, they seem to just work.
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Old 03-28-2019, 05:36 PM   #15
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Quote:
Originally Posted by lynes.nathan View Post
JRaef, which VFD do you recommend as a replacement for the Leeson's?

We actually do have some of those Sterling motors and come to think of it they do last a long time.
Normally I will suggest Allen Bradley drives too and not much major issue but I know I used other brand too it called Fuji or simauir name but I would steer clear of very cheap brands due they dont have much protection at all.

but I havent dealt with 600 volt verison for a while due I am used to 400 or 480 volt system often over here ( in Philippines ) so I dont know how good they can hold up on that voltage level.
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Old 03-29-2019, 12:25 AM   #16
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Normally I will suggest Allen Bradley drives too and not much major issue but I know I used other brand too it called Fuji or simauir name but I would steer clear of very cheap brands due they dont have much protection at all.

but I havent dealt with 600 volt verison for a while due I am used to 400 or 480 volt system often over here ( in Philippines ) so I dont know how good they can hold up on that voltage level.
If I remember, GE VFDs were built by Fuji at one time, they might still be. FP 600s or something like that, it's been a long time since I've worked with one.

I've connected and programmed about 100 of them over the years, only had one burn up. It was a 25HP model that drove a 30HP motor that was pretty well loaded. It ran in or close to current limit most of the time and eventually it'd trip out on low DC voltage.

Most likely, one of the diodes in the front end had burnt up and it couldn't maintain enough DC voltage to run.

Given the above, I think Fujis are pretty good VFDs.

Since I don't remember programming them, they're likely pretty easy.
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Old 03-29-2019, 06:22 AM   #17
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depends on the panel space available.
If you have room then go with a abb-550 with upgraded display as the drive has built in line reactors and the program is user friendly for new people. If you lack space then go with the allen bradley 5** and get start up assistance on the first drive or ask jref for assistance.
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Old 03-29-2019, 01:14 PM   #18
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Originally Posted by micromind View Post
If I remember, GE VFDs were built by Fuji at one time, they might still be. FP 600s or something like that, it's been a long time since I've worked with one.

I've connected and programmed about 100 of them over the years, only had one burn up. It was a 25HP model that drove a 30HP motor that was pretty well loaded. It ran in or close to current limit most of the time and eventually it'd trip out on low DC voltage.

Most likely, one of the diodes in the front end had burnt up and it couldn't maintain enough DC voltage to run.

Given the above, I think Fujis are pretty good VFDs.

Since I don't remember programming them, they're likely pretty easy.
GE drives were built by Fuji for a while, then they changed to having them build by Danfoss about 10 years ago. Now that they are owned by ABB, I expect that to change if it hasn't already.
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Old 03-29-2019, 08:11 PM   #19
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to the OP have you ever considered motor enclosures?

a proper enclosure will have a bearing the drive shaft will go through or grommets and will shield the motor from debris and water contamination but need to be large enough to allow airflow from the motors cooling fan
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Old 03-31-2019, 11:21 AM   #20
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Panel space is limited so I am stuck with going with a drive that is the same size as these leeson's. We have some Allen Bradley drives on some other equipment so I could justify switching over to them. Part of the problem I have is the other maintenance guys don't like change because that means they have to relearn on how to program it. The thing is once these drives are set up they should last for a while.

We do have some motor enclosers on other motors in the plant. They do seem to help but the QA technicians require us to remove them sometimes in order for the motors to be cleaned. They worry about bacteria growth.
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