This is a lightning arrester from an 11kV power distribution line with an interesting feature to clear itself electrically when sustained current flows through it.
Inside a robust fibreglass insulated core is a stack of MOV's (Metal Oxide Varistors) which have a combined voltage to handle the regular peak voltage of the 11kV supply (presumably 15.5kV peak) plus a safety margin. However, when a higher voltage transient occurs on the line the MOV voltage is exceeded and they temporarily develop a lower resistance which shunts the transient to ground to protect other components on the line.
If an excessive over-voltage occurs or the MOVs start to break down after passing a modest amount of transients then there is a disconnecter attached to the bottom of the unit that will literally detonate and blow the ground cable off the end of the unit for safety. The primary function of this is to prevent the lightning arrester from passing significant current from the normal 11kV supply when it fails.
To achieve the fault detection and clearing, the disconnecter has a resistor in it that has enough mass to pass transients without heating up excessively, but when sustained current through it causes it to heat up it ignites an explosive charge that physically blows the assembly apart and lets the ground cable fall down away from the arrester, thus breaking the circuit.
At this point the arrester should be investigated, as the base is not designed to have a sustained open circuit 11kV leakage across it via the MOVs.
One of the most intriguing things about the insulator is that the water shedding disks are made of a silicone rubber material that makes the unit quite rubbery and floppy feeling, but makes it resistant to impact, thermal and UV damage.
In the video I deliberately trigger the explosive charge by applying 240V across a disconnecter. The internal resistance of around 75 ohms allowed about 3A to pass giving an internal dissipation of about 750W. This caused the unit to detonate after a few seconds. I did the experiment with the disconnecter under water to absorb the impact, contain the bits and avoid making a huge explosion in the neighbourhood.
Inside a robust fibreglass insulated core is a stack of MOV's (Metal Oxide Varistors) which have a combined voltage to handle the regular peak voltage of the 11kV supply (presumably 15.5kV peak) plus a safety margin. However, when a higher voltage transient occurs on the line the MOV voltage is exceeded and they temporarily develop a lower resistance which shunts the transient to ground to protect other components on the line.
If an excessive over-voltage occurs or the MOVs start to break down after passing a modest amount of transients then there is a disconnecter attached to the bottom of the unit that will literally detonate and blow the ground cable off the end of the unit for safety. The primary function of this is to prevent the lightning arrester from passing significant current from the normal 11kV supply when it fails.
To achieve the fault detection and clearing, the disconnecter has a resistor in it that has enough mass to pass transients without heating up excessively, but when sustained current through it causes it to heat up it ignites an explosive charge that physically blows the assembly apart and lets the ground cable fall down away from the arrester, thus breaking the circuit.
At this point the arrester should be investigated, as the base is not designed to have a sustained open circuit 11kV leakage across it via the MOVs.
One of the most intriguing things about the insulator is that the water shedding disks are made of a silicone rubber material that makes the unit quite rubbery and floppy feeling, but makes it resistant to impact, thermal and UV damage.
In the video I deliberately trigger the explosive charge by applying 240V across a disconnecter. The internal resistance of around 75 ohms allowed about 3A to pass giving an internal dissipation of about 750W. This caused the unit to detonate after a few seconds. I did the experiment with the disconnecter under water to absorb the impact, contain the bits and avoid making a huge explosion in the neighbourhood.
very informative video
Thought the guy was screwing with me the other day when I couldnt open my garage door at 4am snd he said the lightning arrestor needed to be replaced on a cold night with no storms.
I can believe him now. Our lightning arrestors are right by a fuse line for circuit surges as well and I assumed they were just resetting a fuse line. Guy was a bit rude not understanding why I was bothering him at his job 4am Jan1st soooo….
I remember watching this video shortly after it was posted and I've always thought it a cool design. So, you can imagine my delight when I found a blown 36kv arrestor on the sidewalk while I was out running. It's an all ceramic model, complete with black scorch marks and a partially melted brass connection. I suppose that lightning storm last night was rather serious.
Should send you one for ham radio coaxial
..rock solid hard .. now that's an image
Thumbs down for ads. You dont deserve to be paid for uploading videos
On the railway we went for silicone insulator sheds because they are more resistant to people taking a pot shot at them.
Lightning Arrestor
that little metal disc in the wreckage looked like it might be part of a shotgun primer or something like that
Happy new year! Just had a lovely person try and drive themselves home and run into a power pole. We were treated to an impromptu fireworks display as about four of these arrestors went off during various stages of the repair presumably from the inrush as things were hooked back up. Out here in the rural midwest you can hear these go off from miles away, sometimes several seconds after a brownout or blackout.
have you seen one with a Infrared camera. bad arrestors get thermal resistive heat and glow in the dark.
Can someone do a vid of one blowing up in open air
Things that go boom are interesting until it happens at home
You should let me have that lightning arrester, I need it for my electrical utility collection!
For faster detonation what about a really dangerous capacitor bank? I designed a defibrillator tester a few years back and they have to absorb 600J in a few milliseconds. So of course we had to test it! Unfortunately I'm not sure 600J would be enough for your explosive bolt. It sounds like you used around 10x that from mains.
It's quite a daunting spec: 10 millifarads at 1000V for 5kJ. Then there's the release mechanism to design!
Interesting with the explosive disconnect. The ones we use in NZ haven't got that, and basically blow apart or split open on the side. Just picked one up this morning from the skip and will do an autopsy on it.
"I'm glad I didn't take a Dremmel to it" one year later, he takes a dremmel to one while drunk. then explodes TWO on his table like a moron.