OT ...one for the sparkies

[mark]

[The Real Doctor]

is.

But that aside, since the helicopter gets brought to the same potential as the power lines, I presume this is high voltage DC transmission. I wonder where it is?

Ian

[Frank Erskine]

[geoff]

In message , mark writes

Yeah, it's been posted several times over the past couple of years

[geoff]

Canada IIRC

[John Rumm]

Got a US flag on his shoulder... could be the Massachusetts end of the line from Ayer in the US to Quebec:

[terry]

Doubt if it is DC. Most transmission lines in NA are AC as far as I know, especially since the Canada-US systems are intertwined and share power on linked grids. This is the scheme where a helicopter borne worker first hooks on then transfers himself to the live transmission wire in order to work on the connections, separators, insulators etc.? Thre is some talk of transmitting electrical power from the proposed Lower Churchill generating site in Newfoundland, Labrador across to the island portion of that province, then some 80 miles across the Gulf of St. Lawrence to Nova Scotia, New Brunswick and New York State. Due to the long underwater link would think DC would be used there; with converters at each end. By the way. In that vein (DC underwater cables); anybody know the answer to this question .....? "There was or is a DC power cable across the north of the North Sea beween Scotland and Norway????" Purpose of which to share power between those two countries which have hydro generating capabilities. Seem to remember reading about it in the mid 1950s.

[neverwas]

"There was or is a DC power cable across the north of the North Sea beween Scotland and Norway????" Purpose of which to share power between those two countries which have hydro generating capabilities. Seem to remember reading about it in the mid 1950s.

ISTR the cross-channel link to France was the announced as the first UK-Europe power sharing. And that seems to be confirmed by a quick Google which brings up the history here with no mention of Scotland until 2001 to NI

[Huge]

One of the comments says "This video footage was taken at Beltzvillelake located about 3 miles East of Lehighton, Pa."

So nothing to do with Canada.

[The Natural Philosopher]

No way.

Yes. I visited it in the 60's and it was as far as I know the ONLY external grid link in the UK at that time, and as far as I know still is.

Things that stand out from the visit.

- a room, a very large room FULL of thyratron valves ..each one about 8 foot tall.

- about 6 acres of capacitors to smooth the output.

- Some inductors the size of houses for the same purpose..

- "we can draw a 30KV arc off the line for several hours after switchoff" from the engineer showing us round.

A technical marvel, and JUST ABOUT worth it economically.

I found a couple of references to linking the Orkney and Shetlands using undersea cables (under consideration): Currently the largest is IIRC in the USA ad is 65m long. National grid had(has?)plans to do a half a billion quid one of a gigawatt capacity to Holland. That is the same order of cost as a half gigawatt power station..

Cost are somewhere near a million quid a mile. More for larger power levels like the above.

No references to any scotland Morway links tho.

[Si]

In message , mark writes

[The Natural Philosopher]

I think its for real, but whether the cables are on, and whether you can do more than make a cursory inspection, if they are , is a moot point.

The arc drawn looks clearly DC...sort of what might be left on a 132KV line if the contactors flipped out.

[PCPaul]

Just for reference...

[soup]

I am sure it is real the circuit is not complete (no earth) so NO current will flow. seem to remember watching a documentary about this (the "linesman" stayed on the helicopter platform though) it was "just" an inspection but there seemed to be no fear of touching the wires. C.F. Birds CAN sit on power lines without getting zapped (or there would be lots of dead bird bodies under power lines) but the difference in voltage gives them a slight tingle which they don't like so they tend not to perch on power lines.

Isn't the arc caused by current flow from the helicopter ? Helicopters can work up a fearsome static PD hence the guys that attach loads to military helicopters touch the load strop with a grounded pole first. In a SAR situation allow the winchman to touch the ground/sea first do not try to grab him (he will probably have some sort of "earthing wire" running through his harness). If your life depends on it grab the strop or WHY and take the belt, it is non lethal it just can be very painful A thread that talks about helicopter static build up:-

[The Natural Philosopher]

Thiose isolators are NEVER opened under load though. They have oil filled contactors to actually break the circuits. Those are isolators..thats just redsidual cable capaitance being broken.

[Andy Wade]

You sure? If it were DC the helicopter would just charge up to a constant voltage and the arc would cease - no further charge to transfer, unless there's corona discharge from the rotor tips, or unless it's very ripply DC (unlikely with polyphase rectification).

That arc seems fairly sustained, as you'd expect with AC , and a 120 Hz buzzing seems to accompany it.

[Andrew Gabriel]

I saw a detailed write-up of that (and I've got a much better quality video of it). It's a sulphur heaxafluoride (SF6) breaker switch, not oil. The nearest SF6 breaker is half jammed, leaving the isolator as the only means of breaking it. When the SF6 breaker fires, you see the arc flash across the half of the SF6 breaker which does open, because the other half is still jammed closed. That starts the arc across the isolation gap.

This switch switches the line inductors in/out at the end of a long transmission line which are correcting for the line capacitance. It's not actually carrying the line current.

[Dave Liquorice]

There is more about that arc if you dig about on the web rather than the few words on yewtube.

stuff.

[<me9]

It definitely had the buzz of 60Hz mains. I'd expect more of a crack from DC. It was more like the zzzzz you get when racking a circuit breaker. Scared the s*** out of me the first time I had to do it.

[Huge]

Indeed. Thank you!