# 300 HP VFD Short Circuit Fault



## Big John (May 23, 2010)

The whole point of your surge tests is that the traveling wavefront will stress incipient turn-to-turn and groundwall failures. Usually they're done at several times the working voltage of the motor, so I would really think that would've flushed out any problems. What was the max EAR and max shift on the zero crossing?

Have you ruled out driven load binding? Is it possible to get a fast capture PQ meter on this to prove it's in the drive?


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## John Valdes (May 17, 2007)

Rob, If that motor ran that long without issue I doubt its the control. 6 years is a long time for caps to sit. But you guys were able to run this for what now 2 years?
Did you guys slowly build up until you got to the oprating voltage before adding a load? Most times only a motor shop can do this as many people do not have a variac.
I have been cautioned many times about this. About old caps and old drives that have sat for long periods of time.

Its possible that the drive could be at fault. But my money says its the motor.
How many times (2 I think) can I count this fault report, bring it into the shop and cannot find any problem. 
Baker surge test, high pot test and equipment that can read ohms in 6 figure resolution and still we could not find the issue. And we were the motor shop!

I hate to say this, but you got two choices. Try a new control or try another known good motor that is running on a VFD.
The VFD is better at finding motor issues than most all motor shops. And much, much better than anyone without the equipment I mention above.
I'm afraid you got to bite the bullet and swap to see which one is the culprit. I would swap the motor if it was me. This is past experience talking.

Since the drive ran for two years without issue, my bet is the motor. No matter the test results in the field. I have had this happen to me twice. Each time it was the manufacturer that indeed did find a motor issue.

Please lets us know what you find as this is quite interesting for me especially.
You will get it figured out.


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## telsa (May 22, 2015)

In such brutal service - figure on the motor having reached the end of its designed life.

I can scarcely believe that it's megging out strong.

Is DIRT getting past some seals ?


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## JRaef (Mar 23, 2009)

If you are losing the caps, the load current will have bearing on effects it causes in that under a higher load, the DC bus ripple will increase and if the caps are compromised, your scenario of misfiring of the transistors is definitely a possibility. If you can correlate the trip evens to loading, you might be able to vet that out as a possibility.

That said, I'm pretty sure an ACS800 will have a separate way to detect and trip on excess DC bus ripple. IIRC it will show as a "Phase Loss" trip. I'm not at my PC to look at the manual, I'm going strictly by memory and I may have compromised those brain cells over the years. If you have the manual, look in the troubleshooting section at the criteria for the Phase Loss trip and see if it mentions excess DC bus ripple as a possible cause. If so, I'm pretty sure that would trip _before _it gets so bad as to cause a transistor misfire.

Other possibilities if not the motor:
Load wiring / water in conduit. Being we can assume this is somewhere near Fernley, water in the conduit is a more remote possibility, but if there is a wash plant involved it increases that possibility. Ironically, if the load is LIGHTER it often makes that more likely to happen because with higher load and more heat, a smallish amount of moisture evaporates. But running it lightly means it doesn't create as much heat in the conduit and the moisture infiltrates the insulation. Tripping in the morning after a cool night is a good indicator of this.

A cracked IGBT inside of the drive. I have had that happen 3 times, twice on ABB drives. The IGBT still functions, but under higher junction temperatures the crack widens enough to where you get tracking to ground. You can see it as little black feathery marks on the heat sink that look like they are coming out from under the IGBT.


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## JRaef (Mar 23, 2009)

Did a quick search to find a manual:


> SUPPLY PHASE
> (3130)
> 3.06 FW 2 bit 0
> Intermediate circuit DC voltage is oscillating
> ...


That's what I thought. It's unlikely that a ripple of less than 13% would cause a misfire of the transistors.


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## Jhellwig (Jun 18, 2014)

Does it just give a short circuit fault or does it give more info about the fault. If it saying it is a short circuit on lead u,v,or w it is likely a motor problem. A low ohm meter might show a resistive imbalance or you might have to see if it has an inductive imbalance or preform a ric test.


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## Cow (Jan 16, 2008)

I had an ACS800 throw a similar fault a few years ago as well. It was for a 200HP turbine pump. I megged the wiring and motor and didn't find any low readings. The motor was a newer motor as well. I believe the troubleshooting guide in the manual pointed me towards either a motor/wiring issue or an internal drive problem. Since I couldn't find an issue with the motor or wire we took a chance and replaced the drive. We haven't had an issue since then.

I'd replace the drive.


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## micromind (Aug 11, 2007)

Thanks for the replies, I'll be at the plant either tomorrow or Wednesday and see what has transpired. 

Good info, really helpful.


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## John Valdes (May 17, 2007)

Had you not


Cow said:


> I had an ACS800 throw a similar fault a few years ago as well. It was for a 200HP turbine pump. I megged the wiring and motor and didn't find any low readings. The motor was a newer motor as well. I believe the troubleshooting guide in the manual pointed me towards either a motor/wiring issue or a drive problem. Since I couldn't find an issue with the motor or wire we took a chance and replaced the drive. We haven't had an issue since then.
> 
> I'd replace the drive.


I would see if the drive runs without the motor first. In my past experience, drives are excellent judges as to motor health. 
If the drive is a standard volts/hertz, it should run without a motor connected. Try and see. 
I know its harder to change out the motor vs swapping out the control?
But you need to isolate one or the other. 
My money is on the motor. Disconnect the leads at the control and see if you can start it and run up the speed from the keypad.
Keep us posted Rob.


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## JRaef (Mar 23, 2009)

John Valdes said:


> Had you not
> 
> I would see if the drive runs without the motor first. In my past experience, drives are excellent judges as to motor health.
> If the drive is a standard volts/hertz, it should run without a motor connected. Try and see.
> ...


Good suggestion, and as a step 2 to that, take along a small motor, even a fractional HP, as long as it's the same voltage rating. Make sure the drive is in V/Hz mode and run that small motor with that drive. If it is a major drive problem it would likely show up regardless of the motor size. That would not 100% rule out the drive if it works, because it MIGHT be related to the current flow. But if it DOES fault on Short Circuit with the small motor, you would KNOW it is the drive.


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## mitch65 (Mar 26, 2015)

We had a similar issue to this on a crusher a few years ago. the alarm that came up was similar Short or fault short something like that . What we found when we watched was that the drive would run fine until they loaded it up then it would last a few minutes and go down with she short fault on the display. I put an ammeter on the leads and found it was actually going over current and then tripping. If you watched as it happened, the OC indication would come up and then be replaced by the short indication. 
Only found out about the OC trip by looking in the trip history. turns out they had changed the gearbox on the crusher and the shiv on the new gearbox was bigger causing the motor to OC trip. Guess having to get a 4" longer belt to get running again wasn't a clue that something had changed.


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## micromind (Aug 11, 2007)

I spent the day at the plant and found some new info. 

The crusher is a vertical impact type that can have 1 or 2 motors. When it was first installed (at a different place in the plant) it had 2 motors. It ran for a few seasons then it was replaced by a cone crusher. 

A few years ago, a different cone burnt up its motor and since the impactor was sitting idle, they used one of its motors. It's still running fine. 

The new application is smaller rock and doesn't need both motors, in fact, the single motor rarely exceeds 80% torque. 

The second VFD is buried in a warehouse so while they dug it out, I went home and got my variac, a transformer, a resistor and a bridge rectifier. The DC bus is easy to get to so I spent the day reforming the capacitors, among other things. 

Presently, the caps are around 650 volts, I'm going to leave it that way for a few days, if I can.

The basic plan here is to continue to use the existing VFD until A...... it fails completely or B......they can schedule a day to replace it with the spare one. 

I also told the plant guys to not spend a lot of time in front of it.........lol. Start-stop and speed control are outside the building. 

I'll keep everyone posted as new things happen. 

I like the idea of connecting a small motor to it, there are a few spare 15s and 20s that are still in boxes. Having the crusher down for any length of time is difficult though.


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## wildleg (Apr 12, 2009)

finally . . . a real electrical thread :thumbsup:


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## JRaef (Mar 23, 2009)

So, the original system had two motors and two VFDs, now you are only using one motor and one VFD? Did I get that right?

One odd possible issue might be that in the original system (if I got that correct), the drives would have needed to be coordinated so as to not have one do all the work and drag the other along as a load. When I do this for VSI manufacturers what I do is to set one drive up as a speed follower "Master" and the other as a torque follower "Slave" off of an output torque signal from the Master. So the controller tells the master what speed to run, then it tells the Slave to match its torque and they share the load fairly equally. In going to one motor, if the one they decided to use was set up as the torque follower slave, and they put the analog speed control signal into it assuming it would follow the speed, a rapid change in that speed command could result in the drive attempting to rapidly change the output torque, which is very difficult to do and might have resulted in it trying too hard and tripping itself on what looks like (to it) a "Short Circuit", which is actually just an excessively aggressive change in current.


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## micromind (Aug 11, 2007)

Yes, it used to be 2 motors and 2 VFDs, now it's one motor and one VFD. 

When I discovered that 2 motors and 2 VFDs were used at first, I thought of this as well. The VFD presently in use is programmed as the master (I assume the spare one is the follower but I haven't looked yet). 

I can see how trying to control torque, especially with a large rotating mass, would result in current spikes. When I get back to the plant, I'll look and see what the AI actually does. I'll also look at ramp rates.


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## micromind (Aug 11, 2007)

Update;

I spent yesterday replacing the VFD with the spare one that used to control the second motor. Since they had other stuff for me to do as well, I did't finish until this morning. 

We started the crusher at around 10AM and poured the rocks to it. It was still running when I left at 3:30PM. 

Interesting side-note; the motor is 363 amps and the old VFD would usually run between 310 - 340. The new VFD was 260 - 290 with roughly the same rock fed at roughly the same rate. Possibly the output transistors on the old VFD were misfiring to the point of feeding the motor garbage enough to cause the current to increase?


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