500 KV - But I'm sure it's perfectly safe!

[Bill, KD0HG]

http://www.youtube.com/watch?v=HcalasGr_uk

[The Slab Bacon]

thankz, but no thankz!!

[KB2WIG]

the marrage part scared me....   klc

[David, K3TUE]

I'm intrigued.  Where do I sign up?   

[W1TAV]

I actually saw this being done in South Eastern Massachusetts last fall.  The local newspapers ran articles so the folks would be aware of the work being done. In any event it was VERY unsettling to watch these guys in action!  Although I thought is might be a neat way to get my dipole a little higher.

[W2XR]

Great video!

Yup, this kind of live-line maintenance has been done for years in this country for high voltage transmission lines; I seem to recall reading that it was first implemented back in the early 1960s. In fact, helicopters are also used for installing preassembled transmission towers in those locations where access may be a problem, and this type of work was first pioneered by the Europeans in the late 1950s.

Sometimes, a small "car" that rides across the conductor pair for a given phase is used by the lineman to traverse the span between towers. In the video, the lineman is seen crawling across the conductors for that particular phase; I've never heard of that being done.

I think the highest transmission voltage used in North America is now +/-500 KV DC. It is widely used in Canada for hauling power from Northern Manitoba (Manitoba Hydro) to load centers in Winnipeg, etc., and for inter-ties between major grids in the Minnesota/North Dakota and Oregon/California regions. The high voltage conversion equipment for three-phase AC to DC conversion and back to three-phase 60 Hz AC is incredible to see! It is now done almost exclusively electronically, and without any rotating machinery, with equipment built by Asea Brown Boveri (ABB), etc. .The AC to DC and DC to AC conversion losses are less compared to equivalent AC transmission lines when considering the radiation and power factor/reactance losses for very long transmission distances; this is the primary reason why DC is used for these circuits.

I believe the highest AC transmission voltage in North America is 765 KV, and this has been in use since the late 1960s by AEP in Ohio and Indiana, etc.

The limiting factor in power transmission capacity (known as ampacity) of these high tension lines is the heating of the conductors due to their inherent resistance, and the attendent irreversable stretching and resulting sag of the conductors due to thermal expansion of the cable!

High voltage power engineering is cool stuff!

73,

Bruce

[KB2WIG]

There is a 765KV running from Hydro-Quebec into the US.   It is interconnected to the  NY State grid at  Marcy, and the power is switched into NY City on lower level lines........  klc

[Bill, KD0HG]

Can't do that around here because of the thinner air and corona problems.
IIRC the max is 115 KV AC for lines that cross our mountainous areas.

They've been using Edison's DC for some big western power projects because the peak voltages (and losses) are lower than on AC lines, and you don't get a VSWR effect on long lines that can further jack up the peak voltages. The pylons *do* look strange, having only two conductors hanging on them and not the customary three.

There is a huge AC-DC-AC tie run by WAPA in western Nebraska that connects the midwest to the western grid. From the air, you can see all these transmission lines converging near Sydney, Neb like a big spider web.

[WA1GFZ]

imagine the hardware to convert it to 60 hz.

[Bill, KD0HG]

They've got two-story high SCR stacks that there's circular stairways around!
And king-sized harmonic traps and inductors to filter the trash out, or it would be like a light dimmer wiping out half a state with hash.

Strappin!

I have always wondered what it would take to try to synchronize the 60 Hz between the grids in different parts of the country, but I don't think it's possible. Since the NY blackout of 1977, they've installed underfrequency trips on the systems, breakers start opening if the system frequency drops below 59.9999 (or whatever) Hz.

On the big scale, it's not overcurrent that indicates a possible system overload, it's that a whole grid starts dropping frequency; the generators are unable to hold 60 Hz. So if they tried to link two grids, one would have to slow down a fraction to synchronize with the other, which would be a problem.

When I worked for the Denver electric company, they had some serious frequency counters on the system. The biggest single electric load in this region is the CF&I electric arc steel mill in Pueblo, CO. When they drop those electrodes into the melting pots, you could see the line frequency dip a small fraction of a Hz across the Rocky Mountain states as 6 gigawatts of generators all grunted in unison.

Another awesome-to-behold thing is if and when a large fossil fuel power plant trips off line. You've got these boilers superheating steam to *red hot* levels, and nowhere for that energy to go. So what they have is large pipes from the boilers up to the roof, in the event of an emergency shutdown, valves open to release the steam upstairs where it shoots up a thousand feet or more, along with a wailing sound you can hear for miles. I heard about them testing the emergency shutdown at a 400 megawatt plant out in rural Colorado, supposedly, the noise freaked out the cows at a nearby dairy farm and dried them up for a week..

[W1ATR]

That's from a movie called "Straight Up". It a documentary on helicopters, and the jobs they're used for. Pretty interesting if that's your kind of thing.

[n2bc]

I used to occasionally work at the Robert Moses generating plant in Niagara Falls, NY - late 60's.  Got the complete "cooks tour" one day from the Chief Engineer.  They were testing 750KV equipment in the switchyard & had quite a collection of exploded gear. There was a test-only link between the main station on the Niagara gorge and the Pump/Generating station a couple miles away.

The CE told me that the scariest thing he ever saw was the completely dark switchyard the evening of the big Northeast blackout in '65.  Robert Moses was the second station to trip off.  Biggest problem was they needed power to open the penstocks.  They retrofit two of the generators with pneumatic actuators to open the doors and get those generators spinning again.  It was pretty neat, totally mechanical.

I was installing a data acquisition system that linked the 8 major generating stations of the NY Power Pool together - kind like closing the barn door a bit late....  But, it was 40 years ago and they hooked the stations together with "high speed" lines, all 4800 baud of high speed.

73, Bill  N2BC

[Bill, KD0HG]

Bill, that's one lesson that was learned from that blackout. Generating stations need a lot of power just to get started and running. Coal plants need conveyors, crushers, blowers and electronics to run.

What they did here was set up a hydro plant in the mountains which is designed so that it can be self-sufficient, all mechanical like they did at Niagra. Basically, they pull the cork and let the water flow out through the turbines with gravity. In addition to providing a source of peaking power, it's supposed to provide the power needed to jump-start the power plants in the Denver area in the event of a NY-style blackout.

[W8KHZ]

Interesting video! Here's a similar video, but this guy could use a little more work on his technique!

http://emuse.ebaumsworld.com/video/watch/12307


Brian - W8KHZ