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Registered Member #4081
Joined: Wed Aug 31 2011, 06:40PM
Location: UK
Posts: 139
How do you think the energy got to ground? If it used the standard wiring in the apartment surely it would do something similar, starting fires and such. But I don't know much about apartment wiring. Maybe the plumbing?
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
Awesome Bert! Thats incredible.
BTW, can anyone explain why there is a green flash when lightning strikes overhead wires? I used to think it was because the copper in the wire was being vaporized (burning copper is a green flame), but i think most distribution wire is aluminum, not copper.
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
Any idea of who captured that strike? Was it a person filming or a stationary camera? Seems like a very high resolution camera being at the right spot at the right time.
Registered Member #3282
Joined: Wed Oct 06 2010, 05:01PM
Location:
Posts: 224
Bert wrote ...
Microwatt wrote ...
how much energy do you think was expended in the cable?
Interesting question! I created a small spreadsheet to ballpark some numbers. I assumed that the support cable was made from 3/16" diameter stainless steel 302 cable. based on the building total height of about 20 stories (to top) and 10 feet/story), I estimated that the distance between buildings was about 400 feet. It looks like the stroke connected at a point 170 feet (short length) and 230 feet (long segment). Assume both ends of cable are solidly grounded. The electrical resistivity for SS 304 electrical is 72 microohm-cm, so the estimated resistance of the short segment is ~0.79 ohms, and the long segment is ~1.05 ohms. I guesstimated peak current and duration for "typical" positive and negative polarities using data from Bazelyan and Raizer's "Lightning Physics and Lightning Protection". For a negative CG strike, I assumed that the first return stroke peak current was 50,000 A, and its duration was 100 microseconds. For positive CG lightning, I assumed a peak current of 200,000 A and duration of 500 microseconds. Following is the estimated Joules/segment (simplistically asuming that cable resistance stayed constant vs temperature), and the estimated temperature rise for each cable segment for negative and positive CG strokes:
If "typical" Negative CG strike: Wshort = 50 kJ in shorter segment Est Temp Rise: 17.3 C Wlong = 40 kJ in longer segment Est Temp Rise: 9.7 C
If "typical" Positive CG strike: Wshort = 5.16 MJ in shorter segment Est Temp Rise: 2415 C Wlong = 3.87 MJ in longer segment Est Temp Rise: 776C
YMMV, but based upon the above results, it looks like the higher peak current and longer duration of a positive CG lightning strike is necessary to account for the observed results...
but the cable burned up obviously there was higher than your calculated results. anybody find what the ignition temperature of steel is? we can use simple math to find out how much power was injected/ from the results alot more than 10MJ seems to be used.
Registered Member #3900
Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600
Evr, I think it's some other part of the wire(maybe grounding that carries form each pole down to the ground).
When lighting struck he lines outside my house, it shorted the leads of the nearest pole pig, and the line power followed through. He pole pig exploded with a green flash of he transformers windings itself, and metal rained down on my driveway 150ft away.
Microwatt, the steel isn't burning, so theres no need to factor in auto ignition. When the temperature rises so fast, the metal is still expanding while it liquidizes, which is why in part the droplets fly everywhere. It's also to do with the current still trying to flow through the liquid, and later the chain of droplets.
Registered Member #187
Joined: Thu Feb 16 2006, 02:54PM
Location: Central Ohio
Posts: 140
I don't want to sound like a jerk but I'm a little skeptical about that whole thing. Something doesn't look right. Then again, I have nothing to compare it to so I have no Idea how it should look!
Registered Member #2939
Joined: Fri Jun 25 2010, 04:25AM
Location:
Posts: 615
Someone was videoing the storm and got lucky. It is entirely possible that the burning shower is not metal at all, and is in fact burning plastic from insulation covering the wire(s). That would require a lot less energy. If you step through the video you can see a dark line remaining in the middle of all that fire, suggesting (to me anyway) that there is still an intact cable there.
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Natural Exploding Wire - a massive Russian lightning bolt vaporizes wire connecting two buildings
