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Old 04-22-2012, 08:56 PM   #1
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Talk about living life on the edge


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.'

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http://www.dailymail.co.uk/news/arti...#ixzz1spBXQymz
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Last edited by gregzoll; 04-22-2012 at 09:13 PM.
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Old 04-22-2012, 09:04 PM   #2
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Talk about an adrenaline rush...those fellas are incredibly brave to do that work.

Killer post.
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Old 04-22-2012, 09:19 PM   #3
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Doesn't look all that bad - nobody is grounded.....
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Old 04-22-2012, 09:28 PM   #4
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*BINGO*
You hit the nail right on the head !

But most people dont have a good understanding of electricity,
so they dont understand how they can get away with it !

They can still draw a pretty arc !
But the current would be low.
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Old 04-22-2012, 09:36 PM   #5
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However, not only is the power line live - carrying 230,000 volts - but they are also fixing it from a helicopter which flies inches from the line.

So, what do you think - is this line to ground or line to line
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Old 04-22-2012, 09:40 PM   #6
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At some point some dumbass CEO is going to force them to use cranes in order to save money.

I would totally want to try that though, it looks like a lot of fun. (with the copter, not a crane. )
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Old 04-22-2012, 10:02 PM   #7
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So, what do you think - is this line to ground or line to line
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 3 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.

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Old 04-22-2012, 10:11 PM   #8
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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?
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Old 04-22-2012, 10:16 PM   #9
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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?
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Old 04-22-2012, 10:21 PM   #10
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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.
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Old 04-22-2012, 10:47 PM   #11
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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?
Yes. It's called SWER (Single Wire Earth Return).

Kinda funny, but true; if the lights get dim, go out and pour some water at the base of the pole. They brighten up to normal.

There's some of that around here too, mostly farms way out in the middle of nowhere.
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Old 04-22-2012, 10:50 PM   #12
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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.
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Old 04-23-2012, 08:22 AM   #13
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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.
i worked on a generation project with a 500 kV generator step up transformer. counting space for the CT stack inside the transformer (i believe there was seven), the bushing was something like 20 ft long (oil filled). i want to say it weighed on the order of about 10,000 lbs. those bushings were the single longest lead time item on the entire transformer (500 mva at the second forced cooled rating). core, tank, etc. was all formed up well before the bushings arrived.
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Old 04-23-2012, 08:34 AM   #14
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i worked on a generation project with a 500 kV generator step up transformer. counting space for the CT stack inside the transformer (i believe there was seven), the bushing was something like 20 ft long (oil filled). i want to say it weighed on the order of about 10,000 lbs. those bushings were the single longest lead time item on the entire transformer (500 mva at the second forced cooled rating). core, tank, etc. was all formed up well before the bushings arrived.
Yes, bushings on transformers and breakers are longer than the ones on towers.

The 230KV one I did had the CTs in their own can between the transformer frame and the bushing; they were about 2' long and 2' diameter.

The insulators (bushings) were about 7' long and weighed 760 lbs. They are oil filled.

The bushings on the SF6 circuit breaker were only about 5' long. They are dry type. Each pole came as a fully assembled unit.

The insulators out on the wood poles were about 4' long.
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Old 04-23-2012, 08:46 AM   #15
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Yes, bushings on transformers and breakers are longer than the ones on towers.

The 230KV one I did had the CTs in their own can between the transformer frame and the bushing; they were about 2' long and 2' diameter.

The insulators (bushings) were about 7' long and weighed 760 lbs. They are oil filled.

The bushings on the SF6 circuit breaker were only about 5' long. They are dry type. Each pole came as a fully assembled unit.

The insulators out on the wood poles were about 4' long.
i got involved with this when i noticed the order of the bushing CTs did not match the drawings. there were two CTs on there for differential protection and they were configured such that the two differential zones would not overlap. CTs were adjacent to each other so what would the chances be of a fault in the bushing, between the adjacent CTs, such that neither differential would pick up? purists were saying the bushings needed to be pulled and the CTs restacked. keep in mind the transformer was already on site, in the northern urals region of russia...in winter. winter field modification of CT stacks on 500 kV transformer bushings? sign me up!
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