One of our plants has numerous 100HP and 300HP ABB VFD's (both ACS600 and 800 Series). Our plant power is 460/277V. The drives operate off the 460V line. They run cooling gas blowers for our batch processing equipment. These cooling blowers normally run 1 to 2 hours followed by 6 hours off. We have been experiencing violent VFD failures randomly for about 2 years. Some VFD's are running when they fail. Others have failed while they were waiting for the next run period. Most, if not all of the failures seem to be associated with the VFD DC Bus. The last few that I have personally seen evidently arced through air from the positive to the negative bus leg. The VFD front end MOV's, and the output IGBT's are usually not affected. We have had the power company and an independent power quality engineer monitor our plant power at the incoming switchgear as well as at individual VFD locations for weeks at a time. They have seen nothing abnormal on their instruments even when a VFD has failed during the monitoring period. All grounding has been checked and verified to be good. We have replaced the normal VFD cabinet air filters with high efficiency filters than filter down to about a micron, and change them regularly. Has anyone ever heard of this type of problem before?
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Multiple ABB AC Drive Failures 1
- Thread starter 45bob
- Start date
Now that I read the direction this is going, I have to concurr with the graphite dust theory. At first I wasn;t thinking of graphite as being conductive...duh!
I once had a large soft starter with recurrant SCR failures on a Banbury Mixer, a large machine used to pulverize blocks of raw rubber prior to it being melted for tire manufacturing. The soft starter was located in the same room as the mixer, and carbon black dust from the rubber mixing process was everywhere. Even though we used a NEMA 12 sealed (IP65) enclosure with a bypass contactor and NO ventillation, no enclosure seal that we could find would keep it out of the starter, it was too fine. It would eventually build up enough of a layer on the insulators of the SCR stack that they would conduct to the backpan (ground) and cause the SCRs to short. I can see the same thing happening to your drive, and I especially like itsmoked's "flash tube" theory. Makes sense to me.
"Our virtues and our failings are inseparable, like force and matter. When they separate, man is no more."
Nikola Tesla
I once had a large soft starter with recurrant SCR failures on a Banbury Mixer, a large machine used to pulverize blocks of raw rubber prior to it being melted for tire manufacturing. The soft starter was located in the same room as the mixer, and carbon black dust from the rubber mixing process was everywhere. Even though we used a NEMA 12 sealed (IP65) enclosure with a bypass contactor and NO ventillation, no enclosure seal that we could find would keep it out of the starter, it was too fine. It would eventually build up enough of a layer on the insulators of the SCR stack that they would conduct to the backpan (ground) and cause the SCRs to short. I can see the same thing happening to your drive, and I especially like itsmoked's "flash tube" theory. Makes sense to me.
"Our virtues and our failings are inseparable, like force and matter. When they separate, man is no more."
Nikola Tesla
Thanks for the star! <grin>.
Now for a solution.
45bob; The only solution I see for your many installed units is to fill your drives with positive pressure. This will absolutely prevent further ingress of the evil dust.
You can install a compressor with a dryer and run an air line to your many VFDs.(If you don't already have plant air you can dry) But wait! You say, "How do the drives get cooled if they are sealed with sheet metal??"
You use "Vortex Coolers'. They work every bit as well as the many makers profess they do. They work better than that, in my experience.
Vortex Coolers take compressed air and convert it into two streams, one hot and one cold. You of course, then use the cold to your advantage. Hence, you can deliver serious 'coldness' anywhere you need it down a compressed air line.
You solenoid control the air to each Vortex Cooler so it is only on when the drive is on.
You also set up each VFD with a positive pressure regulator from the same air supply lines to keep each VFD's internal pressure a tiny bit above room air pressure. (inch of water column)
I would guess this solution including labor would probably cost less than replacing a single 300HP drive.
Check these links on vortex coolers, there are many others!
Now for a solution.
45bob; The only solution I see for your many installed units is to fill your drives with positive pressure. This will absolutely prevent further ingress of the evil dust.
You can install a compressor with a dryer and run an air line to your many VFDs.(If you don't already have plant air you can dry) But wait! You say, "How do the drives get cooled if they are sealed with sheet metal??"
You use "Vortex Coolers'. They work every bit as well as the many makers profess they do. They work better than that, in my experience.
Vortex Coolers take compressed air and convert it into two streams, one hot and one cold. You of course, then use the cold to your advantage. Hence, you can deliver serious 'coldness' anywhere you need it down a compressed air line.
You solenoid control the air to each Vortex Cooler so it is only on when the drive is on.
You also set up each VFD with a positive pressure regulator from the same air supply lines to keep each VFD's internal pressure a tiny bit above room air pressure. (inch of water column)
I would guess this solution including labor would probably cost less than replacing a single 300HP drive.
Check these links on vortex coolers, there are many others!
May I sound a note of caution? If graphite is such a problem, why don't dc motors (especially totally enclosed ones) flash over more regularly? Marke's comment about ionisation struck a chord with me, I have seen busbar flashovers caused by less major arcing nearby. Possibly this secondary site is affected by dust build up.
Good point tho 45bob didn't say he had any DC motors, I don't think. Plus he's blowing VFDs like fuses but hasn't mentioned the motors as a failure point yet.... But you bring up a good point, that if he were to implement a solution like the above one I mentioned, it would be prudent to look at other equipment that might soon start falling to the dust too and include them in the repair.
Vortex coolers are great, but a word of caution. Look carefully at the air requirement specifications. It can be a lot of air. I once had a project for drives on an aluminum smelter pot line crane, and it was going to take 7-1/2HP of compressed air to keep a 25HP VFD cool.
"Our virtues and our failings are inseparable, like force and matter. When they separate, man is no more."
Nikola Tesla
"Our virtues and our failings are inseparable, like force and matter. When they separate, man is no more."
Nikola Tesla
Tangent Warning! Red Flag if you think this is getting Off Topic!
UKPete, was your DC motor reference because the brushes on DC motors are graphite, and being so would be cause for frequent flashovers if it were a problem? If so, I see your point but I think that by nature, the dust that comes off of a brush rubbing on the commutator of a DC motor will have already been somehow chemically changed by being involved in an arc while in normal operation, so that dust is essentially "spent" graphite as far as conductivity goes. I have been told that if you drive a DC motor externally for a long time without applying electic power to it, you can in fact build up a coating of conductive graphite dust and have it flash over when you do energize it later. I learned that when working on a maintenance crew for DC elevator motors in a high rise. We were experimenting with AC motors and vector drives, but they wanted to leave the DC motors in place until the technology was proven. They made us remove all the brushes from the DC motors for that exact reason.
"Our virtues and our failings are inseparable, like force and matter. When they separate, man is no more."
Nikola Tesla
UKPete, was your DC motor reference because the brushes on DC motors are graphite, and being so would be cause for frequent flashovers if it were a problem? If so, I see your point but I think that by nature, the dust that comes off of a brush rubbing on the commutator of a DC motor will have already been somehow chemically changed by being involved in an arc while in normal operation, so that dust is essentially "spent" graphite as far as conductivity goes. I have been told that if you drive a DC motor externally for a long time without applying electic power to it, you can in fact build up a coating of conductive graphite dust and have it flash over when you do energize it later. I learned that when working on a maintenance crew for DC elevator motors in a high rise. We were experimenting with AC motors and vector drives, but they wanted to leave the DC motors in place until the technology was proven. They made us remove all the brushes from the DC motors for that exact reason.
"Our virtues and our failings are inseparable, like force and matter. When they separate, man is no more."
Nikola Tesla
ugh.. that's a lot of air.. May not work.
I was trying to avoid the obvious of moving all the VFDs out of the area or individual A/C's. There's always chilled water, with it's humongous specific heat. How about bolting a water block onto the VFD heat sinks, ah-la water cooled PC Pentiums etc.
Interesting point on the motor brushes too. Could be that carbon is coarser and/or is always blown away by armature fans before landing.
I was trying to avoid the obvious of moving all the VFDs out of the area or individual A/C's. There's always chilled water, with it's humongous specific heat. How about bolting a water block onto the VFD heat sinks, ah-la water cooled PC Pentiums etc.
Interesting point on the motor brushes too. Could be that carbon is coarser and/or is always blown away by armature fans before landing.
hi jraef, yes I was referring to the brush dust inside a dc motor, they do get filthy inside and yet the brushgear insulators don't flash over. But 45bob should suspect contamination and follow the good advice given above.
My comment was prompted by a recent 400V 3-phase AC busbar failure I saw initiated (we think) by a small handtool left on top of a busbar above a 4000A circuit breaker. The handtool was partially melted but main area of damage was however a major flashover to earth on the supply side of the breaker, which was physically below and about 12" away. All I'm doing here is suggesting that the primary cause of failure MAY be removed from the obvious damage because of ionisation of the air. I am sure there are a lot of similar anecdotes out there.
Going back to my dc motors, typically 300V or 600V, flashovers did occur due to commutator problems etc and when they did arcing damage could often be found in unexpected places within the motor, usually where the airgaps were smaller (which is why they often used to put sacrificial arcing studs on the side of brushgear adjacent to the frame to give a preferred path to earth when there is a commutator flashover). Ok, I am going off topic now.
My comment was prompted by a recent 400V 3-phase AC busbar failure I saw initiated (we think) by a small handtool left on top of a busbar above a 4000A circuit breaker. The handtool was partially melted but main area of damage was however a major flashover to earth on the supply side of the breaker, which was physically below and about 12" away. All I'm doing here is suggesting that the primary cause of failure MAY be removed from the obvious damage because of ionisation of the air. I am sure there are a lot of similar anecdotes out there.
Going back to my dc motors, typically 300V or 600V, flashovers did occur due to commutator problems etc and when they did arcing damage could often be found in unexpected places within the motor, usually where the airgaps were smaller (which is why they often used to put sacrificial arcing studs on the side of brushgear adjacent to the frame to give a preferred path to earth when there is a commutator flashover). Ok, I am going off topic now.
ozmosis
Electrical
- Oct 12, 2003
- 1,794
Graphite dust doesn't always cause catastrophic failures in drives due to major flashovers. Sometimes you can get localised arcing that does not actually cause major failures but due to the energy involved during this localised arcing, can actually cause the drive to malfunction (the on-board processors and gate-board have some immunity, maybe not enough if the localised energy is high) and in some cases the gate-firing sequence can misfire. The potential of the IGBT's misfiring, if this happens, would be the cause of major destruction and very difficult to pinpoint. We found this to be the case on a site in China recently and it took some detailed analysis to actually find the root cause.
Conformal coating seems to have solved the problem (6 months now with no major explosions whereas before it didn't last 4)
Conformal coating seems to have solved the problem (6 months now with no major explosions whereas before it didn't last 4)
I think that there are probably periodic flash overs in brush type motors. The reason they are not seen is that they are "Self clearing" (the carbon quickly vaporizes to a non-conducting compound (carbon dioxide?)) and the short is only present for a short time (the high speed trip on most drives takes 5 to 10 microseconds to initiate a trip).
I say this, having seen thousands of returned brush type servo motors used in milling machines. One common failure is "Tracking" where brush dust has created a solid short from the brush gear to the motor frame. The most common motor failure, for reference, is brush dust in the bearings.
I say this, having seen thousands of returned brush type servo motors used in milling machines. One common failure is "Tracking" where brush dust has created a solid short from the brush gear to the motor frame. The most common motor failure, for reference, is brush dust in the bearings.
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