VFD Over Current Trip

It sounds like a reflective wave issue because of the long cable run.If you have a local isolator near the motor, try switching off that isolator and note the amps on the drive.It should be close to zero but if its high then thats the problem.You can try decreasing the switching frequency to prove this as well.

A good answer from an AP? Eh? Why would one do that?

Hello Cuba Pete

Many of us started as AP's, earning many GA's, until we thought it wouldn't hurt to have a record too.

Regards

I am the one who gave the AP a GA doofus!

Cheers!

Hello,

The drive trips during motor OFF state too..Load current during OFF trip was recorded as 5 A..Let us consider the 5 A is due to capacitive effec of cable and still 5 A is too less for tripping..Would you pls suggest regarding swithching freq modification its presently at 3.5KHz

Presumably the cable to the motor has been 'meggered' recently, and passed the test?

Heelloo..

The motor and its cable both have been meggered and found normal,they are working normal with another standby drive

we have this same scenario from my previous employer, i am sure that the igbt's are all fine..the problem lies in your triggering circuit.

Hello..

Would you pls what steps have you taken in your previous plant to solve dis one..

We r planning to change the entire igbt module on the suggestion of service engineer and is costing almost 90% of drive cost

Thanks for the reply. But in your case as u said the drive would trip continuously if a IGBT is shorted through heat sink..Here the drive runs fine for some time and then shows up suddenly over current trip..It runs fine for hours to even days some times with outa trip..and some time trips even when drive is idle not running!

Swap it for the strategic spare in the stores, and either send it away for repair or buy a replacement.

• "... But in your case as u said the drive would trip continuously ..."

I never said that, you read something into what I said. I said IF it is leaking any current, it will trip. It could be leaking current via a carbon trace left behind from a more catastrophic failure. But that does not mean it is leaking continuously. There may be a myriad of environmental and situational contributing factors involved in it, so sometimes it happens, sometimes it doesn't.

Bottom line, the signs point to a either a malfunctioning IGBT, or magical thinking about ghosts in the machine. You take your pick

What type of cable are you using? If its not XLPE does vacon recommend a filter on the load side.Try dropping your switching frequency to 2KHz and see if the problem goes away.Note,a lower switching frequency can cause other issues but it may prove that this a classic case of reflective wave form.

Check the cable run (300m !) and make sure it is screened properly and that the screen is grounded at the VFD side. The 5A when OFF is possibly enough to trip the drive because it expects a zero current at that stage. Where is the 5A current coming from? Either the igbt is fulty, or its drive circuit is faulty or the cable is picking stray voltage enough to drive a 5A current ???

Hello Everyone,,

I have observed few things which i felt sharing,,

As we felt the excess cable length of nearly 300m was a concern here,,We isolated the cable from drive and found drive still tripping with Over current fault ( Under same condition of drive being in OFF state, ie IDLE State)

While the cable was isoalated, the drive output voltage was found 50V, and after connecting cable with motor back drive output voltage dropped to 6v), These were observed during drive OFF state.It takes a current of 0.5 A

My doubt is why is drive producing a ouput voltage of 50v even when it is off?

The drive runs fine for some time and suddenly trips showing over current both the times when it is running and stopped time.

The fault history data shows a normal current but still trips,,

Service engineer suggested IGBT module is malfunctioning and needs to be replaced which equals the cost of a new drive,

We procured a new drive instead of a module and trying to find the cause for this,

Suggestions pls,

well, since you have procured a new drive and going to try it, then if the new drive operates correctly without tripping as before, under the same conditions, this would have prouved that the old unit was faulty!

If the fault persist, then ??

Quoting myself earlier:

• "If it is tripping when the drive is in the OFF state, it will typically trip on ANY amount of current flow, because the expected amount is zero. So it CANNOT be anything associated with the load wiring, motor windings etc., it can ONLY be an internal issue in the drive. If one of your IGBT modules is cracked and failing, it could be leaking current to ground (the heat sink itself) across a carbon trace left over from a previous catastrophic failure of the device. A reflected wave issue may have contributed to that failure, but that is not what you are seeing now.
  
  Your drive is toast. Most of the time, the cost to disassemble it to get to the bad IGBT module and replace it might exceed the value of the drive. In addition you most likely will need to replace them all, because if something stressed one of them enough to cause this, the others were stressed as well. This was just the weakest link."

Quoting your recent post:

• "Service engineer suggested IGBT module is malfunctioning and needs to be replaced which equals the cost of a new drive,"

So, you doubted me, now you paid someone to look at it in person and he confirmed what I said, now you are still doubting him? Man, you are a tough sell my friend...

You had a damaged transistor. It was not a complete meltdown, so it only caused a fault under certain conditions, most likely related to heat and stress. If you have thoroughly tested the motor circuit components, i.e. the conductors, the connections, the motor windings, and I do me THOROUGHLY, as in using a megger, not just a multimeter, and you are confident that it was not a reflected wave issue, then you can safely assume it was a random component failure in the drive and get on with your life.

Hello Raef. I read it a long time ago Vacon frequency inverter overcurrent error occurred with the engine as well. Now I have the same situation, but unfortunately for me the inverter should fix it. You may not remember what the transistor was wrong? I suspected from the IC. Thank you in advance for your help. Sorry for the mistakes, I'm Hungarian. Welcome to WordPress. Gabor