Multiple ABB AC Drive Failures
Multiple ABB AC Drive Failures
(OP)
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?





RE: Multiple ABB AC Drive Failures
The reason can also be that your deceleration ramp is much faster than the fan can run down if not braked. Try to make the ramp a lot longer or connect braking resistors.
The fact that drives seem to have failed while not running is a complication. Do not understand that one.
Also, there have been cases where high capacitance resonates with the motors which results in high voltages. But that usually requires PFC capacitors connected to the motor and I cannot imagine that you have that - large filter capacitors perhaps, but no PFC capacitors.
I would check these:
Ramp. Make it as long as is practical.
Wind driven? Watch the fans and see if they ever run above setpoint. Or if they run when not started.
PFC or filter capacitors on motor side?
Does a brake resistor help?
Gunnar Englund
www.gke.org
RE: Multiple ABB AC Drive Failures
I have seen similar things occur when particulate matter builds up. Even if not normally conductive, humidity can bring on enough conductivity to cause a tiny current that rapidly (read instantly) drops resistance so the mains can bridge the path, then KAPOW!. It seems to happen in DC situations a little more frequently.
So check for dust/powder/moisture.
RE: Multiple ABB AC Drive Failures
"Our virtues and our failings are inseparable, like force and matter. When they separate, man is no more."
Nikola Tesla
RE: Multiple ABB AC Drive Failures
RE: Multiple ABB AC Drive Failures
Certain other manufacturers have their heat sinks extending out the back of the VFD enclosure with a cooling blower there. Outside air does not get into the electronics portion of the cabinet. We've begun to buy this sealed type of VFD for all new projects.
RE: Multiple ABB AC Drive Failures
http://www.kooltronic.com/
RE: Multiple ABB AC Drive Failures
One of my experiences was the inside of refrigerated rail car control panels. Sealed, closed, latched. I place a control board inside the panel, unfortunately it was horizontal. The metallic dust given off by the compressor and fan contactors slowly built up on my board until.. well never mind. It was ugly. My psychiatrist sez I should keep it bottled up.
The dust problem does align with units that have energized busses and are on standby doing nothing. Especially if the fans are not windmilling as mentioned by skogs.
RE: Multiple ABB AC Drive Failures
RE: Multiple ABB AC Drive Failures
RE: Multiple ABB AC Drive Failures
RE: Multiple ABB AC Drive Failures
RE: Multiple ABB AC Drive Failures
I've been thru this kind of thing a number of times and each time the problem was, in fact, the incoming power quality but the recording equipment is not fast enough to catch the short transients.
I suspect you will find that the DC bus voltage jumps up occasionally and that is only due to incoming power. If it jumps up high enough--well you know, it goes bang.
As an ABB rep, I find the 600 and 800 series drives to be very rugged. When a situation like yours comes up, something powerful is the cause. Graphite powder is always a problem but you seem to have taken effective steps to clean up the air. I'd bet on power problems.
RE: Multiple ABB AC Drive Failures
They'll blow if there are spikes with enough energy or stop the damaging spikes if they are short. Or VFD's will continue to pop if voltage spikes are not the problem.
http://www.vishay.com/docs/88301/15ke.pdf
RE: Multiple ABB AC Drive Failures
:)
RE: Multiple ABB AC Drive Failures
RE: Multiple ABB AC Drive Failures
Just thought that I would add my 2 cents worth to the good advice that you have recieved above.
I would doubt that the problem is due to mains bourne tarnsients etc as this is more likely to cause component failure than a breakdown of an air insulation gap. The breakdown voltage of the rectifiers will be well below the breakdown voltage of the air between the terminations.
If the problem was due to mains bourne transients, I would expect to see failurs of the input rectifiers and MOVs. If the problem was due to regeneration, I would expect to see problems with the output IGBTs.
To get a breakdown in the air insulation, generally means that there is some form of contamination or ionization. This can be due to foreign matter or insects etc getting where they should not.
I suspec that you are getting a very fine build up of graphite on some of the insulators. When there is sufficient graphite, a small conductive path forms and there is a small discharge across the graphite path. This of course blow the graphite path clear and it may be difficult to find evidnece of it, but it creates ionized air and this will allow the insulating air to breakdown at a much lower voltage and cause the arc between the DC terminals.
I like the idea of using a swab on some of the insulating surfaces to see if there is any sign of grahite there (before a breakdown!) You may need to coat all exposed terminals with an insulation layer, or put physical insulation barriers in place to reduce the problem The best solution is of course to prevent the contamination in the first place. - I would also check the level of contamination on the pcbs as this may be the next point to blow.
Best regards,
Mark Empson
http://www.lmphotonics.com
RE: Multiple ABB AC Drive Failures
I am only one of several engineers at my company who are trying to solve the Drive failure dilema. Before I posted my question, I had my theory as to the source problem. Now after hearing from all of you, I would like to tell you all the conclusion that I have come to and why I have come to it.
I once saw a Sherlock Holmes (Basil Rathbone) movie in which Holmes is explaining to Dr. Watson how it was that he was able to solve the mystery. He explained to Watson that once you have eliminated all the things that it cannot be, that whatever you are left with, however seemily unlikely, has to be the answer.
In looking at the failures, I asked myself, what are the things that could cause current to bridge a large gap? The only two things that I could think of were, high enough voltage, or ... a conductive path.
Next, I thought, where could a high voltage come from? Only one of two places. From the line, where it should be blowing the heck out the MOV's and rectifiers (and other equipment being fed from the same source); or regenerative voltage from the motor, but that's easily ruled out from the cases where the motor isn't even running.
So, what am I left with? A conductive path! Even though we have taken some substantial steps (high efficiency filters) to try to keep the Drives contamination free, there has been some evidence that some "dirt" still gets through.
By eliminating what I conclude that it cannot be (voltage), I believe that it HAS to be contamination. Possibly very fine graphite dust that gets pulled into the air intake grilles (located at the bottom of the Drive door), which either slowly deposits itself on the Drive components, or which occasionaly is conductive enough to be the path directly through air.
That's my "Sherlock Holmes theory". If anyone thinks that my logic is flawed, please point it out to me.
Once again, allow me thanks all of you... Skogsqurra, Itsmoked, Jraef, Sreid, Drivesrock, DickDV, and Marke for your thoughtful and solid technical advice.
RE: Multiple ABB AC Drive Failures
But. You may have left out some facts (like train leaving from Waterloo station at that time, not Victoria station - to paraphrase mr Holmes). One such fact is that there are many other possible paths where graphite dust can and does accumulate. Paths that probably accumulate more dust faster and that also have similarly high voltage stress - not DC but still high peak voltages. And therefore also should have flash-overs.
Another fact that is easy to forget is that IGBTs and capacitors can withstand a very high voltage before breaking down. The working volts and the maximum transient volts are very different ratings. The latter rating often not available, but (often) surprisingly high.
I have had this kind of problem in large drives and small drives of different brands. We still do not know exactly what happened in these drives. Common failure mode is flash-over in DC link or from DC+ or DC- to ground. Clean environment in all cases. Dirt in inverter in one case.
We are all (I think) very interested in the outcome of your case. Keep us informed. Please.
-----------------------------------------------------------
And now for tonight's tale: Paper rewinder. 6000 ft/min 20 ft wide 150 N/ft web tension. Brake generator unwind, Center roll wind. Web tension with Bofors KIS transducer (strain gauge) and tension controller working on BG current limit. Transducer changed for a new "identical" one. Problem: Heavy oscillation. Everything had been checked when I arrived. And I also checked everything - and it was OK. So, something had happened to the tension transducer part. Everything else could be ruled out (mr Holmes).
Tension signal was said to have same filtering as before. Well - not quite. Old filter was specified as a time constant (900 ms) and new filter as corner frequency. So 900 ms seemed to be equal to about 1 Hz - it was thought. And 1 Hz was chosen.
Snag: Filter corner frequency is NOT same as time constant inverse. Filter angle frequency is. So we changed filter corner frequency to (1/0.9)/(2*PI), which is around 0.2 Hz. And then up and running again. Machine had been out of production for two days...
This should probably be in a thread of its own - but.
Gunnar Englund
www.gke.org
RE: Multiple ABB AC Drive Failures
Where's my star?? hehehehe :)
RE: Multiple ABB AC Drive Failures
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
RE: Multiple ABB AC Drive Failures
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!
http://www.vortec.com/vortex_coolers.php
http://www.exair.com/cabinetcooler/cc_page.htm
http://www
RE: Multiple ABB AC Drive Failures
RE: Multiple ABB AC Drive Failures
RE: Multiple ABB AC Drive Failures
"Our virtues and our failings are inseparable, like force and matter. When they separate, man is no more."
Nikola Tesla
RE: Multiple ABB AC Drive Failures
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
RE: Multiple ABB AC Drive Failures
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.
RE: Multiple ABB AC Drive Failures
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.
RE: Multiple ABB AC Drive Failures
Conformal coating seems to have solved the problem (6 months now with no major explosions whereas before it didn't last 4)
RE: Multiple ABB AC Drive Failures
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.