Nice arc

Horizontal Jacobs Ladder?

Cheers

It really scared the chit out of the guy taking the video.

only if the supply is DC

jacob's ladder only ascends because plasma is lighter than air.

Wind? burning insulation creting conductive plasma?

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For a good time: install ntp 

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High wind was mentioned.

My thoughts as well, Probably traveled towards the source. I speculate a failed isolator started it.

Cheers

And it seemed to be mains humming at 120Hz.

I reckon you are right with vapourised burning insulation hanging between two phases to make a self sustaining plasma ball. Odd that their cable insulation burns so well and quickly! We have had ours arc and spark a bit in wet weather sometimes taking out circuit breakers but never anything that spectacular.

Bit of a surprise how fast it moved along the street. I wonder if it would be hot and noisy enough to satisfy the poster in the other thread?

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Regards, 
Martin Brown

Lorentz force always pushes a high-current arc away from the power source - think railgun. Long-lasting arcs can occur when a phase-to-phase arc is initiated across a pair of phase wires through the air, usually by wind-driven conductor movement or a falling branch. The arc may then persist if the upstream breakers fail to open the arc-faulted circuit.

The speed of the arc is related to the square of the short circuit current. In LV and MV power distribution systems, these can reach 10's of kA, creating arcs that literally fly down a pair of lines. The arc may travel for quite some distance along the parallel wires until the upstream transformer supplying the fault current ultimately overheats and fails.

Bert

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Bert Hickman 
Stoneridge Engineering 

You can make "laser produced plasmas" by focusing a nanosecond-pulsed laser down to a sufficiently small focus. Once they form, the plasma becomes absorbing, and so it grows rapidly back along the beam towards the lens.

I used to have a 40x microscope objective with a neat 1 mm hole drilled in its front element by this effect.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
Principal Consultant 

Laser ablation mass spectrometry exploits this method usually NdYAG pump quadrupled as they found UV couples best and smallest spot size.

A few groups have excimer lasers for the same duty. It does away with all the messing about dissolving awkward ceramic samples and can do spatially and depth resolved work if you program it correctly.

It is only slightly short of non destructive testing since in most cases only a tiny spec need be ablated for a quick determination.

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Regards, 
Martin Brown

Yup. Mine were air plasmas, because I was trying to make ionized air for localized use inside semiconductor equipment. (A partly-baked idea of my boss's way back when.) It was actually pretty fun-- I built a Plexiglas box with a couple of grids inside it, which could be charged and discharged rapidly using an 811A triode. It was easy to see the charge dropping stepwise each time the laser flashed. (This was about

1988 btw.) It was also a good illustration of displacement current in action, because you could see the current starting when the laser flashed and stopping again when the charge actually reached the grids.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
Principal Consultant 

Visual reference:

Tim

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Seven Transistor Labs 
Electrical Engineering Consultation 

d? burning insulation creting conductive plasma? I reckon you are right wit h vapourised burning insulation hanging between two phases to make a self s ustaining plasma ball. Odd that their cable insulation burns so well and qu ickly! We have had ours arc and spark a bit in wet weather sometimes taking out circuit breakers but never anything that spectacular. Bit of a surpris e how fast it moved along the street. I wonder if it would be hot and noisy enough to satisfy the poster in the other thread? -- Regards, Martin Brown

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ROFL