Helicopter flies inches from LIVE electrical power lines so daredevil repairman can fix them
But because the power lines serve 400,000 people, the line cannot be closed down, meaning the work needs to be done while the line is live.
Highlighting the dangers of the work, the commentator on the film says: 'These lines are still energised; we are flying right at them in a big hunk of metal filled with jet fuel.'
Transmission lines like that are almost always expressed as line-to-line.
I just finished a substation that was fed with 230KV, the transformer weighed over 100,000 lbs. without oil or coolers attached.
Most of these systems are 3ø and have 3 wires. They're usually wye connected with the center of the wye connected to a ground grid.
the line to ground voltage of a 230KV system is about 133KV. At that voltage the earth is a pretty good conductor. Even over long distances.
For example, the 230KV side of transformer I installed was a wye, the center of the wye was connected to the ground grid at the plant. The plant is about 35 miles from the substation feeding it.
There is a CT (Current Transformer) on the wire that goes to the ground grid, it's connected to a relay that monitors ground fault current, among other things.
When a transformer with a grounded wye primary is first energized, there is basically a short circuit to ground for about the first 1/60th of a second. The ground fault relay can read and record this event, and in this installation the peak current flowing 35 miles back the supply substation was 273 amps.
To work on a line like that hot, you put on a wire mesh suit. If you didn't have one on, the capacitance of you body would flow enough current to kill you even if you weren't in contact with anything grounded.
Interesting info. I have noticed that even single phase applications only have 1 HV wire going into the transformer. So the earth is literally being used as a conductor then?
I live in a rural area where the single phase distribution voltage is 7200 Volts. It is a wye system and the neutral is run parallel with the hot line so there are two wires on the pole. Every transformer on the system has a ground wire down the side of the pole too.
An engineer once told me that you can count the insulating doughnuts that support a transmission line a get an idea of the line voltage. He said each doughnut was good for 10KV. Any truth to this?
Generally true, but some of the insulators are only about 8KV or so. Others are more like 15 or even 20KV. Those are usually on the 345 or 500KV lines.
They don't look it, but the insulators on a 500KV line are about 8' long. And they weigh about 1,000 lbs.
When there is a second wire halfway up the pole, going from pole to pole as a neutral/ground, it is still customary to have grounding electrode conductors at each pole or every other pole going down to ground rods.
Some POCOs do, some don't. Around here, it's every third pole unless there's a transformer mounted on it.
They use grounding plates here instead of rods. Basically, they're a round copper plate about 8 - 12" in diameter that is fastened to the bottom of the pole before it's set into the ground.
I'd like to see the scrappers steal those!!!
Lol.
Silly info; the brand (A round steel or aluminum disc about 1-1/2 or 2" in diameter, usually recessed about 1/2" into the pole) is almost always 12' from the bottom. If you can see the brand on the pole, you'll know how deep it is into the ground.
Just a quick note here, I'll be going out of town tomorrow to connect the instrumentation to a good-sized control panel on an oil refining plant. I'll be gone for about 2 weeks, so when I don't respond here, I'm not ignoring anyone, I just won't have a computer for a while.
There are high power lines about 100 ft outside my 4th floor office. One day I hear a loud engine and look up into the eyes of a helicopter pilot. It appeared somebody was hanging out the otherside inspecting the ceramic isolators. In this case just a fly by. I was hoping to see him climb on the wire.
Interesting, I did not know that's how they worked. That explains their size and shape. I had always wondered why it's not just a basic straight chimney going up.
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Related Threads
?
?
?
?
?
DIY Home Improvement Forum
3.1M posts
320.1K members
Since 2003
A forum community dedicated to Do it yourself-ers and home improvement enthusiasts. Come join the discussion about tools, projects, builds, styles, scales, reviews, accessories, classifieds, and more! Helping You to Do It Yourself!