VFD Buss Overvoltage on ramp up 1

[Kiljoy]

We have a machine in the field with a Yaskawa V1000 15HP VFD installed in it. It is running a conveyor. We are controlling the speed via a 4-20mA signal to the drive which varies from 0-60Hz. We used the canned “Conveyor” setup from the menu.

Here’s the problem. When the customer runs the conveyor at 50% speed (30Hz) or below, it seems fine. When they attempt to go over 50%, they get a DC Buss Overvoltage fault. We are not decelerating during the fault, so we don’t think it’s a regenerative problem. We had them run at 50% and then change it to 60% speed and it trips every time. The supply is constant 482V. We had a line reactor feeding the drive and it appears to have opened a leg. So, we’ve bypassed it for the time.

Everything I’ve read says regenerative problems cause overvoltage errors. But, the problem ONLY happens on the ramp up when we get past the 50% speed mark. I’m kind of stumped here. I even had them monitor the Buss voltage through the drive and it never went past the 700V range. So, something is happening faster than the drive would display. Any thoughts?

 

[Mobius44]

I suspect the VFD has gone bad, perhaps from the same event that opened the leg of the line reactor.

Try contacting Yaskawa, especially if it's still under warranty.

 

[Kiljoy]

I did. I get conflicting suggestions based on who I talk too. The local guy said it’s a regenerative problem when deceling and to add a breaking resistor. I tried to explain that we were not decelerating during the fault and he said to do it anyway. The Yaskawa tech guy said it could be a motor connection problem. The local guy said no.

 

[Marke]

Hello kiljoy

This could be a problem where there is instability in the speed control system which is causing the vfd speed to vary up and down.
This can be due to a problem in the VFD, or a mechanical resonance.
Is the VFD operating with an encoder feedback system?

Best regards,
Mark.

Mark Empson
L M Photonics Ltd

 

[Kiljoy]

No, it's just running a belt conveyor system. The speed display stays pretty constant.

 

[TurbineGen]

Mark is referring to the electrical process. Is there any feed back given to the VFD from the conveyor system? An issue in the feedback loop could cause the VFD to assume a fault condition.

I have to agree with Mobius. It sounds like the VFD might have gone bad.

------------------------------------------------------------------------
If it is broken, fix it. If it isn't broken, I'll soon fix that.

 

[Kiljoy]

There is no feedback. It’s just driving a 15HP motor. Our Yaskawa guy thinks it’s an intermittent ground fault or poor connection to the motor. The end user is trying to find a 30ft. ladder to look in the motor terminal box.

 

[X49]

I once had problems with two 2hp Allen Bradley VFD's that started tripping on bus overvoltage upon any type of acceleration (from 0%). Both VFD's in the facility started doing this at the same time.

They were installed on a stiff 600V system with no line reactors and I suspect they were damaged by surges. Replacing them fixed the problem.

 

[LionelHutz]

Did it work at one time? If the answer is yes, then a good start is to suspect a drive or motor problem. Another possibility is the analog signal has issues, such as momentarily dropping out or dropping to 4mA.

I have seen drives with a failed diode suffer from over-voltage problems. Basically, the diode switching, reactor and capacitor caused a ringing and the peak of the ringing washigh enough to trigger the over voltage trip.

If it never worked, then I'd also suspect something as simple as the belt jumping causing a momentary regeneration.

 

[Kiljoy]

It doesn’t trip unless you go over the 50% speed. I do not suspect an intermittent analog connection as it would randomly trip when at the lower speeds. It does not.

We are going to replace the drive and see if the problem goes away. This is a new installation and I'm not sure if the conveyor had trouble from the start or not. The conveyor is brand new as well. I am working with our local dealer on site. We will be sending our own service guy next week.

 

[LionelHutz]

OK, let us know what the problem was.

 

[Kiljoy]

The problem is dealers and end users that order drives and don't know how to use or set them up ;p Not that I'm bitter or anything... hehehe

I'll keep you updated.

 

[Marke]

I have seen this sort of thing happen when there is mechanical mis alignment in the system which is causing the power to go backwards and forwards.
Best regards,
Mark.

Mark Empson
L M Photonics Ltd

 

[jraef]

I still like LionelHutz's theory, the issue with the signal drop having to do with speed may be caused by extra vibration once you get above 50% speed. Remember, it's far more likely to be the simplest answer than the fringe one.

But we do love the fringes around here... So here's mine:
The belt (assuming rubber based) is stretching under the force applied by the motor against the load carried by it and acting like a "rubber band" where it's snapping back and getting pulled forward in an oscillating manner. If the snap backs get too excessive, the drive regenerates. It only gets excessive when the speed gets above 50%. Simple test, see if it happens with no load on it. If not, keep increasing load until it does.

There is a company called Conveyor Dynamics that makes a living out of the prevalence of this issue in conveyor systems. The founder is a Ph.D in wave dynamics.



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[ozmosis]

It could be an over-hauling load on the conveyor whereby the load drives the motor once it reaches a certain speed and the inertia of the system takes over rather than the VFD. This could introduce an overvoltage.

 

[Kiljoy]

Jraef, Ozmosis;
That’s a very good theory. However, it’s an incline belt, so the coasting theory seemed unlikely to us. But, it does seem probable. Unfortunately, I’ve not been to see the installation. But, from my experience, when you get to conveyors of this size in the recycling industry, they end up being chain driven and often metal instead of rubber. But, I can not confirm that as of yet. I’ve also discovered that the conveyor is brand new and manufactured by one of our other dealers. Thanks for the ideas! We’ll change the drive out Wednesday or so and see if the problem goes away. I and the drive manufacturer do not think it will.