Power Flex 40 shows fault code 13, what should I be looking for?

[leitmotif]

Dan, ya gotta give me more time to edit. I am beaming 256 bytes per minute through a repeater to a cell tower out here!

Heck I figgered you were still shoveling yourself out of the great global warming blizzard.

QUESTION or proposed trouble shooting method to determine VFD ground fault since I still dont have a 1000 V meggar just a 500 V bought dirt cheap from Boeing Surplus.

Disconnect motor and motor conductors at VFD.
Place motor on insulated from ground surface.
Connect motor to VFD with 3 phase conductors only
Energize VFD and start motor
Check motor frame voltage to ground at several speeds say 25 50 75 and 100%

Thoughts feedback?


Dan

 

[OkiePC]

I only got 9 inches of snow but it's mostly gone now. I bet it was 65 degrees today but there was a chilly gusty breeze so I didn't stay out in it much.

If you don't like the weather in Oklahoma, just wait 30 minutes.

 

[leitmotif]

I only got 9 inches of snow but it's mostly gone now. I bet it was 65 degrees today but there was a chilly gusty breeze so I didn't stay out in it much.

If you don't like the weather in Oklahoma, just wait 30 minutes.

Seattle it is five minutes.

The cause of our weather woes is global warming one week El Nino the next.

Dan

 

[Gil47]

This begs the question how does the drive detect the ground fault.

In any drive I have looked at this is achieved by monitoring the current in all three leads out to the motor, using hall effect current sensors, and should they be more than about 20% of full load out of balance they will call an earth fault.
Either because there is a ground fault or an out of balance current situation.

This is normally caused by the motor being faulty in my cases usually wet,
The other alternative is that one of the hall effect sensors is faulty and depending on whether you reach the 20% threshold level as to whether you get a trip.

My money is on a faulty motor.

 

[DickDV]

PLC Kid, there is an ANSI standard around that says to megger a 460V motor at 500V but I find that inadequate even for ATL motors. Shucks, the 460V sine wave reaches 660V twice each cycle which is more than the test voltage. Ordinary NEMA motors are tested at 1200VAC when built.

On inverter duty motors, 1000V is the minimum acceptable in my opinion. As in the case here in this thread, a drive will test the insulation up to 1600V in ordinary service so I don't see where 1000V meggering is any problem.

Yes, my rule is 1000V on 460 and 500V on 230.

 

[Bob O]

Here is a link to a pdf you may like.

http://www.omnicontrols.com/articles/Megger-A_Stich_in_Time.pdf

 

[Tom@Pton]

Dangerous method of checking out a motor. If a VFD says ground fault, believe it. Read the link, get a megger and check the circuit/motor.

 

[leitmotif]

Dangerous method of checking out a motor. If a VFD says ground fault, believe it. Read the link, get a megger and check the circuit/motor.

Completely agree that what I proposed is not a safe method BUT it is testing / troubleshooting which in my mind justifies risk but there have to be controls for unauthorized people. Should have included this in my proposal obviously.

Copied from Gils post
In any drive I have looked at this is achieved by monitoring the current in all three leads out to the motor, using hall effect current sensors, and should they be more than about 20% of full load out of balance they will call an earth fault.
Either because there is a ground fault or an out of balance current situation.

So in effect an imbalance of 20% is interpreted by VFD as ground fault? Sorta makes sense - especially if VFD is also monitoring output voltage and ensuring they are all the same (120 apart of course)

Hmmm alternative method
put clampon around all three VFD outputs and check for low level current reading? Would clampon be able to detect and display this? May be difficult for small motors ie less than 20 HP??

Dan Bentler

 

[oreo1]

With the motor mounted to the frame and the ground wire connected to the motor, use a 1000V megger and test the insulation from where they are removed from the VFD, all the way through the motor. I normally clamp all three motor leads in the ground clamp at once and then touch the probe on ground before activating the megger. If there's a disconnect/terminal box/other terminations involved, you will be proving them all at one time, preferably before disturbing them. I have seen disconnects with ground faults that go away when you jiggle the handle, or open the box, and then return in the middle of production.

You need at least 2 megohms for a PF4 or 40 in v/hz mode, but I have seen some drives tolerate less, while others like some Toshiba G7s I have, that want over 100megohms to avoid tripping for ground faults.

I suspect you will read much less and find a damaged wire or motor winding. If you get a low reading, leave those wires off the drive, separate them from the motor leads and repeat the test.

The wiring, open at both ends, should read infinity or as near as your meter can to that, and the motor should read above 2 megohms.

The VFD is trying to protect you from a serious shock hazard. There is dangerous potential reaching the case of the motor, I would be 80% sure it's in the motor, at least inside the peckerhead, but prove it with a megger to be sure, and test the motor leads while you have the tools out.

DON'T apply 1000v meg test to wiring that is connected to the VFD.

It is remotely possible that the tech is seeing a carrier frequency induced voltage when the ground is removed, but the fact that the drive sees a ground fault...most likely the drive is right.

I agree with everthing mentioned above, I folowed every step and after thousands of dollars on parts and all it came to vibration where the disconnect was installed, repositioned the disconnect onto the machine wall and the problem went away. We tested the conductors, used the a different vfd and the problem could be only replicated with vibration.

 

[OkiePC]

I agree with everthing mentioned above, I folowed every step and after thousands of dollars on parts and all it came to vibration where the disconnect was installed, repositioned the disconnect onto the machine wall and the problem went away. We tested the conductors, used the a different vfd and the problem could be only replicated with vibration.

Is this the solution for the original problem which started this thread?

If so, thanks so much for coming back to update it.

Paul

 

[leitmotif]

Thanks for posting the fix.
Most interesting

Dan Bentler

 

[OkiePC]

... the problem could be only replicated with vibration.

Megger the disconnect all by itself. Jumper from top to bottom so you can check for ground leakage between the lugs and the enclosure while you operate it, jiggle it, Fonzie it etc.

I had a big 800A square d stainless disconnect switch that started causing ground faults on a Toshiba. It ended up being traced down to a cracked insulator between the operating bar and the knives. When we took it apart and finished breaking it, there were carbon trails through the crack. We had to bandsaw it and stick the pieces in backerdz with the seams away from the knives and use a remote lockout procedure while I hunted down (and I say that literally) a new insulator...which got us by until I could replace the whole thing.

 

[DickDV]

Am I understanding that this disconnect is in the leads between the drive and the motor?

 

[OkiePC]

Am I understanding that this disconnect is in the leads between the drive and the motor?

That's how I am reading it. In this facility, almost every motor has a local disconnect at the motor (wired between drive or contactor and motor).

 

[The Plc Kid]

That's how I am reading it. In this facility, almost every motor has a local disconnect at the motor (wired between drive or contactor and motor).

Same here but we have the motor disconnects with a early make NO contact that closes when you begin to put the disconnect in the off position and this stops the drive first before the leads are opened.

The procedure is to stop the motor in question by it's normal SOP but we have these contacts in the disconnect just in case. After all it's a jubgle in here and anything can happen.

Our people can manage to destroy a Sherman Tank if you put it on the production floor.