Damaged Yaskawa VFD is being blamed on me

[skbutler]

I installed two new identical Yaskawa VFD Model CIMR-P7U47P51B-107 to drive new identical 10 hp 480Vac 3ph motors. This was as simple an application of VFDs as you get. No network control, nothing unusual. The only problem I had was terminating the signal wires that connected the two units so they could communicate with each other. The wires I used, at the factory's rep's suggestion was a short piece of Belden cable that came with the pressure sensor. The wire was 18 awg stranded. Two of the terminals required nesting two wires in the terminal. Due to the very small size of the terminals and the angle I had to work, it was next to impossible to fit 2 wire into one terminal and make it look professional. After I had completed the installation and had both units running perfectly, I decided to go back and replace the Belden cable with stranded wire with Belden cable with solid wires. PLEASE no need to comment on this next step. I took both units to local and turned unit B off but did not de-energize the VFD. (I know, I know.) My hands were far enough away from a hot terminal that I wasn't worried. I removed the stranded wires and was in he process of inserting the low voltage solid wires when BOOM. I got slammed backward. I was out for maybe 30 seconds. The VFD was fried. The three 60 amp fuses were all blown. After removing the VFD and replacing with a new unit I photographed all terminals and all external metal surfaces to show a complete lack of any arc mark and shipped the unit back to Yaskawa. They sent back a two page report (form style) that concluded "IGBT blown gate drive board and the DC bus capacitors damaged. Input phase R, S, T open at + side. S, T open at -side. Damage to the unit indicates that an external source caused the damage to the IGBT." Since they have the unit I can't verify any of their findings. But I know I didn't do anything to cause the unit to blow. I am a boiler expert, not a VFD expert even though I'm an EE. If an "external source" caused the damage, shouldn't there be some external physical indicator? Opinions would be welcome.

 

[skbutler]

Hey people, don't you know it's Fat Tuesday??

This is the down side to smart phones. It's Mardi Gras, I'm in the French Quarter of New Orleans. There are so many people on Bourbon Street that it takes 20 minuets to cross the street. There are at least 700,000 people on Canal Street waiting for REX. And I'm setting in a bar emailing eng-tips on my iPhone with the gang screaming at me to PUT THE PHONE DOWN... we're going to the Show Bar!

How do you say 'I just gave them the finger' without it being offensive?

Ok ok.... a few things before I geaux.

ischgl99... the only person who could fire me is me. I did think about it and I gave myself a stiff warning. And there was a lot of finger wagging involved. I guess technically the owner of the company could fire me but he would rather sell one of his daughters than fire me. So what can you do.

jraef ... good post but you leave put one thing. You are sure exactly what I did or if I've stated it accurately. I am very sure of what I did and didn't do. Occams Razor... a lady in New York flushed her toilet and New York City had a city wide blackout. Even to this day, 40 or so years latter she still believes that Occams Razor's simplest solution is her flushing the toilet caused the blackout.

OperaHouse... Two Excellent posts

waross -- good post. I've just finished writing a book, The HandBook on Packaged Boilers and am in the process of the final edit. The chapter on troubleshooting stresses the importance of the troubleshooter following the customer's (plant's) safety program. There are however time when electrical equipment must be serviced, tested or trouble shooting... trouble shot? [I'm starting to feel that last hurricane. where was I? That's why most safety switches have a mechanism that allows the switch door to be opened without disconnecting the service. I also left one point out, so as not to bias the group. This event occurred about a month after installation. This unit had 497 runtime hrs I think. After the power was first applied, one of the pressure transponders didn't work. The factory rep brought another. I'm pretty sure he had thought there was nothing wrong with the original transponder. As one poster said, it is rare to have an electronic part bad out of the box. The factory rep turned the unit off on the front end panel, 480 still live on the entrance terminal strip but all displays dark. I asked him if he wanted me to kill the power and he said it wasn't necessary. He re-landed the the sensor wires, pressed on and the sensor was still bad. He turned the unit back off (480 still hot) and landed the new sensor wires, cursing the whole time... as I said before, it was extremely awkward to land these wires. He pushed ON, the display lit and the sensor read okay. As a matter the sequence of events, there is no difference between what he did and what I did. This leads me back to my original question. Is it possible that installing the jumpers on the VFD that was powered by 480 but switched off to cause the unit to blow?

To me there is only a limited number of answers to this question:
I don't know.
Yes, you can never install a sensor to a VFD with power in the entrance terminals, it will blow every time.
I have never seen a VFD blow because the sensor wires were shorted or open circuited.

There may be more but now I'm havine to spell check every work I type and it's killing me so I"m going back to the parades or the strip club, which ever I come to first.


oh oh, one other thing. I love these posts and might want to include some of them in the troubleshooting chapter of my book. If I do I'll contact the forum and the individual poster for permission. Each poster is the copyright holder of his or her posts and my publisher is fanatical about copyrights

other opinions still welcome
thnakss steve

 

[jraef]

Is the part about being in the strip club going to be included in the troubleshooting guide?

Have fun but again, don't touch!

 

[rhatcher]

skbutler - I hate to kick a man when he is down but, as Popeye used to say,..."it is what it is..."

The link I've provided is the manual for your drive. On page 30 is the drawing of the terminal strip. Your terminal strip is the one at the top of the page. It appears to be a really small VFD with a really small terminal strip arrangement that has about (you tell me?) 1/4-1/2" between the terminals.

To make things worse, the R+/- and S+/- terminals for RS-485/422 communications (I am guessing that is what you were connecting) are directly adjacent to the +2 terminal (DC Reactor Connection = DC Bus?) and the B1/B2 terminals (braking transistor unit connection).

I am just guessing (I'm not a Yaskawa drive expert) but I would say that the 'B1/B2 - braking transistor unit connection' (ie. dynamic braking transistor) is somehow connected to the IGBT gate firing board. It seems that it would have to be.

There lies the problem. That terminal strip is so small that working on it while energized would be like playing the old 1970's game called "Operation". However, instead of an annoying electric buzzer sounding when you touch the wrong part you are instead 'rewarded' with a big bang. Yes, the factory representave did the same thing but, just because he was careless and got away with it it doesn't justify you doing so.

I will finish by saying that the amount of voltage/current required to fire an IGBT would not leave a trace of arcing damage. Also, you could just as easily fire an IGBT by applying a small DC voltage to the wrong terminal as you could also fire it by applying a ground to the wrong terminal. It depends on the circuit.

So...In my opinion I would say that you are very lucky on several counts (in order of importance):
- you did not injure or kill someone else
- you did not injure or kill yourself
- you did not lose your job
- the damage was relatively inexpensive

A previous poster said that you should buy a lottery ticket because you are so lucky....

I say do not waste your money because you have probably already used up your luck for a while.

 

[sreid]

I'm going to be a contrarian. When you hear Hoof Beats you should think Horses, not Zebras. But sometimes it is Zebras. While we know we shouldn't work on something that's hot we've probably all done it [less as we get older, hopefully].

It could be that the drive just decided to blow at the same time that wires were being changed. Unlikely but possible. And something like this has happened to most of us. We see an obvious cause and effect relationship that turns out to not be true.

And the fact that skbutler got an electrical shock doesn't mean he touched something. When Power Devices blow, the metallic arcs can find you. This happen more than I like to think when were powering up brand new drives in more devil-may-care-days.

 

[rhatcher]

As a requirement of troubleshooting, I routinely work on hot circuitry. I draw the line at 600VAC and 750VDC and when doing this I am very, very, very careful.

Part of this care is not to contact a live circuit. Another part of this care, otherwise known as good judgement, is knowing when it is necessary to work a live circuit and when it is not necessary.

There does not seem to be any benefit to doing what skbutler did by attaching communications cables to a VFD that was turned off but still powered up. In my opinion, that was an unnecessary risk, especially considering how small the terminal strip is and the close proximity of control terminals to power terminals.

Finally, I have to ask since no one else did...How far away was the power disconnect switch from the VFD? I'll bet it was right there in sight.

skbutler is a lucky guy. I have been similarly lucky in the past so I am speaking from experience. It only takes a momentary lack of reason (or lack of judgement, lack of safety awareness, lack of common sense, momentary distraction...call it what you want) to make the difference between another day at work and an industrial accident.

I still don't buy lottery tickets; there is no point since I have used up my luck and am still trying to make up the difference.

 

[rhatcher]

sreid,

Your post appeared while I was typing my previous response.

I like to give people the benefit of the doubt when due and I especially appreciate it when others give me the benefit of the doubt.

Clearly there is no way that we (eng-tips members) can know exactly what went wrong here; we can only surmise on the events as recounted to us by the OP (skbutler).

Your point about the possibility of something randomly blowing up when you happened to be randomly standing in front of it is correct. This is a possible outcome if you are very unlucky.

For me, this has happened maybe once or twice in almost 20 years of exposure. Because of this, I consider myself unlucky because even a once or twice exposure to this type of random and very dangerous failure is 'once or twice too many.' After all, it only takes one time for things to go wrong and to end it all for you.

In addition to random bad luck, I would also add that there have been a few other times that things have failed spectacularly while I was troubleshooting them hot. In these cases, a fault was known to exist and during the course of troubleshooting the fault became 'more evident'. I guess this type of thing goes with the territory when you are troubleshooting a hot ciruit and could generally be considered 'unavoidable' if there is no alternative to troubleshooting hot.

No matter how careful you are, there is always a risk in our field.

So...In this case, skbutler stated (if I read him correctly) that the unit had 497 hours of run time before the fault and that it happened to blow right at the moment that he was applying wires to the terminal strip.

If this accident happened by random chance, meaning a VFD failure unrelated to skbutler's actions or presence, then he is definitely an unlucky guy.

I am certainly willing to give him the benefit of the doubt based on your point of argument. After all, we can not know for certain what happened if by his own admission that skbutler doesn't know what happened.

But...this benefit of the doubt is given based on the idea of an unlikey event happening (ie. random failure at the moment that you connect a wire to a hot terminal strip) as compared to the other, in my opinion, statistically more likely event - human error.

 

[skbutler]

Wow, the long post I just typed disappeared before I posted it. I have a love/hate relationship with this new wireless Apple mouse. Anyway, less than 2 hours till Ash Wednesday. It's hard to imagine but at the moment the French Quarter has maybe 150,000 to 200,000 people in it, 90% drunk and by 1am it will be empty, all bars closed and the Quarter clean. The cops and street cleaners line up on one side of the Quarter and at midnight they start sweeping drunks and trash out of the Quarter. It's something to watch.

Irhatcher said, "the amount of voltage/current required to fire an IGBT would not leave a trace of arcing damage" I'm sure he's correct there but not sure what he's referring to here "To make things worse, the R+/- and S+/- terminals for RS-485/422 communications (I am guessing that is what you were connecting) are directly adjacent to the +2 terminal (DC Reactor Connection = DC Bus?) and the B1/B2 terminals (braking transistor unit connection). " The low voltage terminals are not directly adjacent to the +2, B1/B2 terminals. The R+/- and S+/- terminal strip is elevated 1.5 to 2 inches above the +2, B1/B2 terminals. Has anyone here ever accidentally landed one of the three 480 supply wires to the 120v coil terminal on a motor starter because the two terminals are only 2 inches apart? That not the same thing as landing a wire on terminal 12 instead of terminal 11 which is identical to and next to terminal 11.

This has been a great exchange. I've learned three things:
1. It is very unlikely I caused the failure by making a wiring mistake. The terminals next to the ones I was working on are all analog signal terminals and are all software assigned and were and are all set off. Terminals that Irhatcher referred to are totally different terminal type and 2 inches away. How could I have shorted any of those terminals to each other or to ground. After the unit blew, the jumpers were exactly where I left them, terminated to the proper terminals. I'm not saying I could not have accidentally touched a jumper to the bottom terminal strip. Anyone can make a mistake. If that blew the IGBT it would have done so instantly, correct? Then how could I have installed the jumper?

2. Never get cute with the facts. The fact is I was never in any danger of being electrocuted and in all likely hood I didn't receive an electrical shock at all. I most likely jumped back when the unit blew... it was very loud and smoky. I most likely slammed myself back against the MCC panel and cracked my own hard head. That's what dazed me. I'm very careful when working inside a hot panel. I practice failsafe techniques. That doesn't prevent accidentally touching a hot terminal, it simply means when you do it doesn't kill you. I routinely touch 120v and 240v terminals to be sure they are de-energized. When they are not, I get a little surprise but it can't kill me because I only do it WHEN IT CAN'T KILL ME! But I would never ever suggest anyone else follow my practice. On occasion I will touch a 480 terminal but I have to be standing on a known good insulator, have my rubber soles on and dry hands. Even then touching 480 isn't fun. It's like working off the ground... you can never eliminate the possibility of falling but you CAN eliminate the possibility of falling and hitting the ground by the use of proper safety harnesses.

3. How quick people are to offer help and suggestions and how well schooled in safety forum members are.

Let me leave you with an anecdote to than about. I've been working on boilers since 1973. I've designed systems for chemical plants, nuclear power plants, ship (one Russian) and commercial. I have only had one Honeywell FSG control that was bad out of the box... or was it. I had a customer's Honeywell RM7800L FSG control showing an error code I had never seen. The manual decoded the code as "CallService" That's Honeywell's way of saying the control is dead. A friend at Honeywell told me the code meant that an internal fuse had blown and was not user replaceable. The only external thing that would blow the fuse was the fuel valve circuit. I ordered a new control and proceeded to check out the fuel valve circuit. I could find nothing wrong. I checked all the usual suspects: inrush current, normal current, condition of wiring, the 7800 sub-base... I just couldn't find anything wrong with the wiring. I installed the new control and the instant I applied power, even before the 10 second initialization period started, the control failed with the same error code. I re-examined the wiring. I meged every wire. I installed time delays relays to cycle the fuel valve on and off on 3 minute cycles and used a 3 amp inline fast blow fuse in the circuit. I let it run for 24 hours and no blown fuse. The internal fuse was 5 amp. The new control arrived. The man I work for asked me what I was going to do. I said I had done an in depth examination of the existing system and could find nothing wrong... I was going to install the new control. He said, didn't you say the same thing last time? I said yes I did. The evidence Indicates the replacement 7800 was bad out of the box. He said, You're telling me that the first replacement control failed with the same error the existing control had... an error you had never seen?" Yep, that's what I said. I installed the second replacement control and it worked fine. That was three years ago.
Was that control really bad out of the box?
Was there an intermittent problem that killed both controls and then went away?
Was it just coincidence... a million to one shot?
Think about it. I tell you the answer tomorrow.
Wow, it's Ash Wednesday and I am beat... Mardi Gras'ed out

 

[niallnz]

Don't keep us on tenter hooks... what is the answer to your last anecdote?

Cheers Niallnz

 

[MikeHalloran]

I hope the silence doesn't mean he's run out of luck...



Mike Halloran
Pembroke Pines, FL, USA

 

[ScottyUK]

I routinely touch 120v and 240v terminals to be sure they are de-energized. When they are not, I get a little surprise but it can't kill me because I only do it WHEN IT CAN'T KILL ME!

You aren't immortal. Really, you aren't.


----------------------------------

If we learn from our mistakes I'm getting a great education!

 

[skbutler]

oops, sorry niallnz. I just got home. I will respond post shower.

BTW, there is nothing like a beautiful spring day in New Orleans.

 

[skbutler]

The bad out of the box Honeywell FSG control.
A week after I replaced the second control I received a call from my friend at Honeywell. I expected the call since I marked the two control I sent back to his attention. He asked me how the new control was working and I told him just find. Then he said, 'you know, only one of the controls you sent back was bad. The other control is fine and according to its memory, it has never been cycled since it was manufactured.' I said, 'son of a b*****.' I knew exactly what had happened. I had marked the old control with the date and BAD error code 57 and when I removed the new control from the box I marked the new control with the date and NEW. I had marked the removable face plates on the controls and sat them on a table, separated so I couldn't get them confused. I went outside for a minute and when I came back the Priest and maintenance man were there standing next to the controls. The maintenance man was holding the new control, the one next to the shipping box. Actually the Priest and maintenance man had accidentally switched controls. I replaced the face plates and installed what I thought was the new control but was the original control. After I received the second new control, I shipped the original control and the first new control that was never installed back to Honeywell.'

The reason I marked the face plate and not the control body is sometimes we send FGS controls back for rebuilding and magic markers are hard to remove from the blue plastic Honeywell uses.

See you on the neutral ground.

 

[LionelHutz]

I routinely touch 120v and 240v terminals to be sure they are de-energized. When they are not, I get a little surprise but it can't kill me because I only do it WHEN IT CAN'T KILL ME! But I would never ever suggest anyone else follow my practice. On occasion I will touch a 480 terminal but I have to be standing on a known good insulator, have my rubber soles on and dry hands. Even then touching 480 isn't fun.

This pretty much sums up your safe working practices, or lack thereof. I won't write anything more about retarded practices like this because I'm quite sure it would be considered offensive.