Switch in "Jurassic Park"

Thats probably to make sure the switch throws really fast. You have to do that in order to avoid arcing, leading to rapid heating, leading to your ass getting blasted into the next block.

Luhan

A fecking big spring. This ensured V.fast opening/closing action and avoids damaging or explosive arcing. (Usually there is an interlock to ensure that the switch can't operate until the spring compression ("charge") has reached a set-point.)

Quite a standard feature on a lot of high voltage switchgear, although by no means universal.

This would most likely be a circuit breaker. The spring is used to provide power for closing the breaker, and I think it also retains energy after closing so that it can trip without further charging. These are found on what are technically low voltage breakers, which are rated up to 600 VAC. Then there is "Medium voltage" up to 5000 VAC, and only above that is switchgear actually "High Voltage". So a cubicle with a 4000 ampere breaker on a 480 VAC main feeder should be labeled "Danger: Low Voltage" !

I don't remember that part of the movie. I think most switchgear that is directly operable like that is 600 VAC or less. Above that I think it is mostly operated by means of hot sticks or remote control by means of solenoids or motors, usually from a bank of batteries. Some breakers have charging motors or solenoids, which also usually run on DC, to charge the internal springs. Other breakers have cranks or handles with ratchets to charge the springs, and smaller molded case breakers (about 800 amps or less), generally require brute force to charge the spring when the breaker is closed using the handle. That is why it usually takes more effort to close a tripped breaker than one which has simply been turned off manually.

Circuit breakers are amazing devices, and are certainly more convenient and versatile than fuses. However, it is always a good idea to incorporate fuses in the protection scheme as well. A faulty breaker will often freeze up in its closed position, providing no protection, while a faulty fuse almost always just opens prematurely, and this is usually because of partial melting from a previous fault, or environmental factors such as corrosion. Also, fuses can clear faults with potential currents of 200,000 amperes or more, and actually limit the current to a lower value by clearing in less than 1/4 cycle, whereas breakers often take one or two cycles to clear. This means much more power is dissipated in the arc of the opening breaker, often causing destruction of the contacts and other parts. "Low voltage" breakers are generally limited to 10,000 or possibly 25,000 amperes interrupting capacity, and even within those limits often must be rebuilt after clearing a fault.

I saw a film produced by Bussmann, where they showed the effects of high current faults being cleared by circuit breakers and fuses. With the fuses, in the worst case there was a quick jump of the cables and a puff of smoke where the fuse body ruptured. With the breaker, huge sparks (actually molten metal) spewed from the arc chutes, and at currents well above the interrupting rating, the entire breaker exploded and the conductors violently flew out of the enclosure, and the resulting arc was not extinguished until the upstream protective device shut off power. I wish I had access to that film on-line. It was actually an 8 or 16 mm film, not a videotape.

Paul

Oh, so it's a safety device to prevent the operator from electrocuting him/ herself. That makes sense.

You mean it actually kept on arcing like a welding torch?!

Yes, that's why there is the interlock to prevent closure until the spring is charged enough for a subsequent trip.

Those rating divisions are actually not a global standard. Different countries have different numbers in their local (national) standards.

Not in this country. Here LV is less than 110DC or 32VAC IIRC. So it would properly read "Danger: Medium Voltage"

But that type of message is really for the non-cognoscenti.

Quite a bit of this stuff here in Oz has pump-up springs on 6.6/11kV gear. There is even one brand (nicknamed "Tupperware") which uses a huuuge over-centre spring action with horizontal moving contacts within cylindrical shrouds on their 11kV (and possibly higher rated) gear. The one thing we were taught when operating this - apart from the gloves and flash shield - was to NEVER stand in line with those "cannons" ...

And don't get me started on the old oil-filled HV s**te.

IIRC the loose ends alternately arced to the grounded enclosure and to each other where the insulation melted. The main power was only applied for a few cycles, and mostly there was just smoke, flying debris, thrashing cables, and sparks. I think it was in slow motion.

However, a friend I work with was injured once when his coworker dropped an uninsulated wrench across a main 480 VAC feeder during a circuit breaker testing job, and it apparently caused a short with just enough resistance to maintain a fireball for quite some time before the main fuses upstream finally opened. Both were badly burned, and the coworker who dropped the wrench eventually died. My friend saw the wrench drop and had just enough time to turn away, avoiding a direct blast to his face.

I went on a circuit breaker testing job early in my career, and it seemed safe enough to pull breakers from cubicles, service them, and then rack them back in to the buswork while they were tripped, and only closing them when they were fully locked in place. However, a few years later, someone went to the same site, and apparently one of the stab clusters was loose. While racking it in, the cluster fell across the live buswork, and caused quite a blast. I think he survived with some bad burns. Technicians are usually taught to stand to the side and turn away when racking switchgear.

Paul

be labeled "Danger: Low Voltage" !

Thre's a new requirement in the USA that all switchgear be evaluated for the amount of arc-flash and labeled with the minimum safe distance to prevent sunburn. For the really big switches, they're labeled with the safe distances given various kinds of protective clothing.

On Sun, 2 Jul 2006 02:02:20 -0400, "Paul E. Schoen" wrote: Snip..

Nice write up. I appreciate it. Here are some videos of interest.

http://205.243.100.155/frames/longarc.htm#Disconnect

Regards,

Boris Mohar

Got Knock? - see: Viatrack Printed Circuit Designs (among other things)

void _-void-_ in the obvious place

What was being pumped was your money out of your pocket. ;-)

It's for dramatic effect, so that there's some unknown delay as the monster is closing in on them.

Cheers! Rich

The LA power department has a big test facility, and made a film of their "greatest hits." It looked like the credits background of "Apocalypse Now."

John

Oh, because it emits lots of light, UV and X-rays, right? How do you pull a switch when you have to be far away from it (what if it's outside your reach? even with protective clothing you said there's a "safe distance")?

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I had something similar happen with a 208V 3 phase 200A panel - I was removing a breaker and as I took the screw out, the bakelite piece that holds the breakers in place when the screw(s) are not holding it, and to provide insulation between the phases was cracked and fell away. This allowed the breaker's tab to fall across 2 phases, 12" from my face. Apparently there was quite a deafening "BANG" when it happened. After I got back from the hospital (Checking my eyes, mostly for welders flash, but I had contacts in which may have blocked a lot of UV), where were massive smoke / condensed metal stains on adjacent breakers, the panel, my screwdriver, the tab on the breaker was half gone, and I still never found the screw. I also ended up with a blotchy sunburn.

The guys installing our new 400A feed (which is fed with a shared 1200A transformer - lots of short circuit current available before the feeder fuse blows), with much upgraded wiring work on the (crude) buss box adding wires while *energized* without seemingly much concern. Next time I might make it mandatory to when work on those panels or future larger ones is done de-energized, or with at least some protective gear

Some impressive arcing can be found here:

http://205.243.100.155/frames/longarc.htm