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Small things can have huge consequences! - Printable Version

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Small things can have huge consequences! - Casey - 08-07-2019

Hey everyone! So it's been pretty quiet around here so I just kinda thought I'd share something interesting that happened at work. It's not directly related to Mosquitos(hence why we're in the abstract forums), but the lesson learned can still be applied to lots of aspects of experimental helicopters!

The setup: 

This morning at my place of employment(a small controls and electrical shop) my duties involved helping an engineer of one of our customers conduct a rated current test on a rectifier bridge to be used in a hydro plant as a generator excitation device. Basically in this test we connect a large AC transformer that will supply low voltage but high current to the input of a large rectifier bridge, and we short together the DC output side so that current will flow. We bring the unit up to the maximum current the unit is rated to run at(I.E. 400 amps DC in this case) and let the heat build up and just verify the unit will indeed operate properly at the stated current.

The procedure seemed to be going quite well, however, we began smelling every electricians stomach-knotting smell, burned electrical components! So let this be the first lesson we illustrate here: whether you're flying helicopters, cooking bacon or conducted a rated current test on high voltage equipment, if something doesn't feel, or perhaps in this case, doesn't smell right, then stop what you're doing, shut everything down and figure out what the problem is or just reschedule! If you're gut is telling you something is wrong then chances are pretty good that it's right!

Anyways, that's where this story should stop, but unfortunately, we're not done. After a little investigation that yields no indication of the cause of the smell, the engineer decides to proceed with the test. I don't mind because afterall: A. It's his equipment, so if he wants to assume liability well that's no skin off of my back and B. while it is a very high current we're only running 10 volts AC so the chances of a dangerous arc flash situation are almost non existent. So we continue.

Not surprising, 10 minutes latter the alarms go off and the unit trips and what was once just a hint of a burning smell has now turned into that electricians nightmare: smoke. So now that we have visual cues of not only smoke pouring from the drive cabinet, but also the HMI giving us the warning that we have suffered a main fuse failure.

So in the AC input side of the cabinet where we connect our cables from the transformer to the unit, there exists the 3 fuses that protect the entire unit from an over current condition. These 3 fuses, one for each phase of incoming AC power, are each rated for 400amps, and they are in seriously bad shape!  These are large sand-filled porcelain fuses, and one is cracked and another seems almost burned!

Now I don't want to get too deep into science and mathematics here, but just know that while we were pulling 400amps on the DC side, the AC side would be seeing no more that around 285amps. So there is no way we blew these fuses on overcurrent, but they are most certainly blown!

Well when the fuses finally cooled down enough for us to pull them the story began to unfold. So this customer would order these fuses from a big name manufacturer of industrial fuses, and then would take the brand new fuse and apply their own adhesive label to it with their internal part number to identify it and then install it into the equipment. Now they did not put any thought into what temperature the device that they are applying said labels to would reach. So as the current flowing through these fuses rose, so did the heat as well. I wish I would've thought to get a temperature reading before they cooled down, but suffice to say the adhesive label began to boil and melt. This created a hotspot in the porcelain of the fuse causing it to crack and begin a cascade of failures that eventually led to the element burning out and ruining our test. 

So because this little sticker was not rated for the temperature of the device it was attached to, it literally caused it to fail even though you would think there's no way a little piece of paper would cause a $400 industrial fuse to fail like that! I was amazed!

Now I know that most of you here are far more mechanically inclined than I so I wouldn't dream of trying to "teach" anyone anything lol! But I just figured I would come tell this story as a reminder to all the tinkerers out there that just because a change might be small and insignificant when compared the overall project, but the butterfly effect can be found in a lot of unlikely places! So here we are, a $1200 failure and a customer witness test that is now in danger of being canceled, all because of 3 little stickers!

So my point is, stay safe, think things through thoroughly, and if it doesn't feel right, well it probably isn't right! 

Deuces!

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RE: Small things can have huge consequences! - Eblezien - 08-07-2019

Thanks for the story! That is food for thought and good advice for all us experimental aircraft builders/operators. Safety first. Little things can make all the difference.


RE: Small things can have huge consequences! - jb92563 - 08-12-2019

(08-07-2019, 10:10 PM)Casey Wrote: Hey everyone! So it's been pretty quiet around here so I just kinda thought I'd share something interesting that happened at work. It's not directly related to Mosquitos(hence why we're in the abstract forums), but the lesson learned can still be applied to lots of aspects of experimental helicopters!
...
Interesting story, thanks for taking the time to share it.
What you described is a common notion in Aviation and many other disciplines as to the detail that needs to be observed. 
"Change one thing, change everything" is the rule for aircraft and you see that all the time where what seems like an easy change 
results in a series of dependent/related changes approaching the threshold of a project or rebuild.
Thats why aircraft development takes such a long time and because the tolerance for failures is so low, especially in Helicopters.
No room physically and financially for much redundant systems in a recreational Helicopter, which his why the success of the Mosquito is so special.


RE: Small things can have huge consequences! - CaseyS - 08-14-2019

(08-12-2019, 11:34 PM)jb92563 Wrote:
(08-07-2019, 10:10 PM)Casey Wrote: Hey everyone! So it's been pretty quiet around here so I just kinda thought I'd share something interesting that happened at work. It's not directly related to Mosquitos(hence why we're in the abstract forums), but the lesson learned can still be applied to lots of aspects of experimental helicopters!
...
Interesting story, thanks for taking the time to share it.
What you described is a common notion in Aviation and many other disciplines as to the detail that needs to be observed. 
"Change one thing, change everything" is the rule for aircraft and you see that all the time where what seems like an easy change 
results in a series of dependent/related changes approaching the threshold of a project or rebuild.
Thats why aircraft development takes such a long time and because the tolerance for failures is so low, especially in Helicopters.
No room physically and financially for much redundant systems in a recreational Helicopter, which his why the success of the Mosquito is so special.

Could not have said it better myself!