allen Bradley vfd's ok part 2

[Timboe]

I installed a line reactor on one VFD to see if the problem would go away. It still tripped that night, I checked it in the morning and it faulted on the F5. I have these drives set on auto restart and it max's out to the F33 max restart trys. The weird thing is why don't the other drives fault as well? Its like only a few. Can the MOV get week and close when it shouldn't? or stay open to long and not functioning properly? I'm about ready to give up and just replace the ones that are tripping so the night time guys don't have to reset them every morning. By the way they say they have to try several times to get them to reset then there fine the rest of the day. Meaning they can be stopped and started from that time on until the nexted morning. When i say they have to try several times they reset hit the start and it will trip and they will do it again until it starts. I set the read out so they can watch the bus voltage and they don't see it rise above 680v.

 

[ptonsparky]

Have you changed your ramp times, especially the deceleration? How quickly do you have these responding to speed changes?

 

[petersonra]

I installed a line reactor on one VFD to see if the problem would go away. It still tripped that night, I checked it in the morning and it faulted on the F5. I have these drives set on auto restart and it max's out to the F33 max restart trys. The weird thing is why don't the other drives fault as well? Its like only a few. Can the MOV get week and close when it shouldn't? or stay open to long and not functioning properly? I'm about ready to give up and just replace the ones that are tripping so the night time guys don't have to reset them every morning. By the way they say they have to try several times to get them to reset then there fine the rest of the day. Meaning they can be stopped and started from that time on until the nexted morning. When i say they have to try several times they reset hit the start and it will trip and they will do it again until it starts. I set the read out so they can watch the bus voltage and they don't see it rise above 680v.

the voltage can rise fast enough that you can't see it on the display but it can still trip. you need something on the bus monitoring it that can catch a momentary peak that exceeds what the trip setting is.

it is possible there is some defect in the drives.

sometimes a firmware update is the fix. perhaps a knowledge base search with the vfd model number and the error code is in order.

I also seem to recall that on at least some drives the trip point is adjustable. you might want to check and see what the trip point is set to.

a brake resistor might be helpful as well.

 

[Jraef]

What model of AB drive and /or how old are they? If the are 1336 drives, it could be that the capacitors are failing, causing too much ripple on the DC bus. The display value will average it out, but the protection circuit is absolute.

 

[Jraef]

Missed the editing cutoff...

If they are PowerFlex 4 or 40, those have a built-in CE filter which can sometimes do funny things when the line to ground voltage has issues, especially if it is a corner grounded delta system or resistance grounded. You may need a drive isolation transformer in that case.

Either way, this is likely something that happens too fast for it to be seen on the drive display. If you really want to see it, hook up a recording meter to the DC bus, one that can capture fast transients.

The MOVs do not "close" by the way. MOVs are connected to the line at all times and all they do is conduct extreme voltage spikes to ground. They would have nothing to do with this situation, and when they fail, they just quit working (or blow up).

 

[Timboe]

These drives are power flex 4 and they are old probably 4 or 5 years old. They trip on start up so the brake will due nothing. Why are the MOVs not relevant if they can't let excessive high voltage escape won't it go into the circuitry or wherever else at to high of voltage and cause problems. I thought that is what they do.

 

[petersonra]

These drives are power flex 4 and they are old probably 4 or 5 years old. They trip on start up so the brake will due nothing. Why are the MOVs not relevant if they can't let excessive high voltage escape won't it go into the circuitry or wherever else at to high of voltage and cause problems. I thought that is what they do.

the MOVs start to work well above the point at which you might trip.

the brake resistor does not care whether the motor is just starting up or not. it is operated when ever a higher than expected voltage is seen on the DC bus.

I am not saying a brake resistor will fix your problem but it is relatively cheap and might fix it.

Are any of them tripping when they are not actually starting up? If it is a power problem one would think they would trip regardless of whether the drive is running or not if there is a power issue.

 

[jcormack]

Old?

Old?

I had to LOL at the "old" Powerflex 4 comment. I guess it is a matter of perspective - a Toshiba G1, an AB 1302, or an Emerson Variable voltage controller I would call old. We still have a boatload of 1336, 1336+, 1336 Impact and some Saftronics (pre Yaskawa) drives running in my facilities. A PF 4 that is only 4 years old I would still call a "pup". The PF4 is Rockwell's low-end product - it is considered by some (me included) to be a "throw-away drive", meaning if you are having problems, throw it away & get a new one. Having said that, I have installed several PF 40's that seem to work OK & prefer to use the PF70 for most of my apps - I can see where an OEM would chose the PF4 for it's cost & size - sometimes you get what you pay for. If you have spares go ahead and replace one that is giving you the most trouble - see if the problem goes away or stays - if it stays, the problem is an external issue -either with the incoming power or with your load - is it possible the night shift operates differently? the PF4 and PF40 are availble with a DB built in as an option - it is large enough to help with some powerline or load regen issues - they also have optional internal filters. I would also make the accel and decel a little longer as mentioned by others, this may help if the issue is load related. What is your nominal AC input voltage? does your plant voltage rise at night? As others have said capacitor switching could be an issue with transient voltage spike or harmonic ringing. Do you have any capacitors on the 480 buss that feeds these drives?

 

[Timboe]

The line voltage in this control center is 496 volts. The allen bradley support tech said the drive will not trip if there is not a condition making it trip. Yes I have increased decell time and nothing makes it happen less even the line reactor. He told me that when I put in new drives it will fry them over time also. Now to end this thread I'm just going to replace all the ones that are faulting and not have to worry about it for now. Thanks for all the answers.

 

[Jraef]

The line voltage in this control center is 496 volts. The allen bradley support tech said the drive will not trip if there is not a condition making it trip. Yes I have increased decell time and nothing makes it happen less even the line reactor. He told me that when I put in new drives it will fry them over time also. Now to end this thread I'm just going to replace all the ones that are faulting and not have to worry about it for now. Thanks for all the answers.

OK, but just realize that this does NOT sound to me like it's a problem with the drives. It might be, but I've been in the VFD game for 25+ years now, and this kind of thing is hardly ever a hardware issue.

Other possibilities not yet discussed, because we still don't know how they are being used or how they are connected:

2. Pumps (or blowers) outputting to a common header without back-flow protection, so when some are already running and you add new ones, a venturi effect created by the other running pumps/blowers is dragging the newly added ones beyond their commanded run speed as they ramp up and they regenerate, even briefly, enough to cause the OV trip. But by the time anyone looks at the drive display, it is no longer happening so it looks OK. It could be that the only time anyone does this is in the late shift because the rest of the time, the system is running full tilt boogie.
3. You have long leads from the control panel to the motors, no load reactors or cable terminators, and/or you have them installed in plastic conduit without using shielded power cable, and there are reflected waves and / or induced voltages coming back into the drives, but only some of them because of the juxtaposition of the cables and locations of the motors loads.
4. You have control signal wiring that is improperly shielded, or the shields are improperly grounded and there is noise coming into the board that is getting through to the PC board and causing it to react as if there is an over voltage (usually the faults are more random though).
5. Since they are PF4s, there is some sort of interaction with the CE filter that they have, but you are not telling us anything about your power system, i.e. corner grounded delta, resistance grounded Wye, etc. etc. that might be a contributing factor.

Good luck.

 

[petersonra]

The line voltage in this control center is 496 volts. The allen bradley support tech said the drive will not trip if there is not a condition making it trip. Yes I have increased decell time and nothing makes it happen less even the line reactor. He told me that when I put in new drives it will fry them over time also. Now to end this thread I'm just going to replace all the ones that are faulting and not have to worry about it for now. Thanks for all the answers.

I am guessing you will have similar problems with the replacement drives.

please let us know how that works for you.

496 is kind of high but I don't think that by itself would trip the drives.