Agreed. But this was in the days before wikipedia. The difference really doesn't matter to graduate civil or mechanical engineers, while physicists and electrical engineers would not need to have to have it explained; at least in those days.
Once in 20 years among the adult population does not seem wildly out to me. Especially if you include "tingles" from wet appliances, and even more static shocks to those who cannot differentiate. But I do wonder where the statistic comes from.
No - that's not what they are doing. Those lines are live.
What they are doing is making an equipotential bond between the line and helicopter. The helicopter as basically a conducting object in free air has inherent capacitance to ground and the the reactance is sufficient to cause a not insignificant current to flow at 1/2 mil volts 50-60Hz :)
If the line were made dead, it would have been earth strapped at both ends before anyone was let near it (standard operating procedure).
And for a quicky dodgey calcL
Capacitance of sphere of radius 1m (tiny helicopter) in free space is about 0.1nF
Reactance at 60Hz approx:
1 / (2f x pi x C) = 27MOhmsCurrent at 254kV to earth (440kV phase-phase, for 3 phase) = V/R = about 10mA
Which is enough to hurt and be a danger.
In reality I think the presence of a nearby ground plane (the ground) plus the fact the helicopter is longer than 2m and has lots of sticky out bits is likely to push the current a fair bit higher.
Plus some of those lines you speak of may be higher than 440kV.
So on that basis, whilst a small bird can sit on an HV line, if an ostrich got up there, its feet would probably tingle :)
All other things being equal, the only reason for not having widespread ele ctricity distribution in 2014 would be if the filament lamp had never been invented, which was the original 'killer app' to make public electricity su pply a viable business. The problem before that was "sub-dividing the elect ric light", as in the 19th century, before filament lamps were invented, on ly arc lamps were available, and these were only practical for large output s, so tended to be used with local generators at about 100v DC, 70v being n eeded to maintain an arc in air, the rest for the regulating resistance to limit the current.
Eventually discharge lamps (mercury, sodium, etc) would be developed, but n ot in domestic sizes, these are more efficient on AC supplies, allowing the use of transformer ballasts, so things would have panned out at 440v 50Hz three-phase, for induction motors in industry, stepping down to 110v single
-phase for power tools and discharge lighting, supplied by local generation from natural gas or diesel engines.
In the UK and other countries with natural gas supplies, domestic lighting would be by gas mantles, with no general distribution of electricity, inste ad household thermo-electric generators could be used for powering electron ic equipment at 50v DC, so avoiding the need for shock protection measures, and gas for everything else, with LPG cartridges for portable appliances s uch as irons, places that did not have gas supplies could use kerosene or L PG cylinders.
Are you suggesting that Harry might have posted an article he has not read thoroughly and understood completely?
Probably they got somebody like Mori to carry out a poll, asking a number of statistically average people and extrapolating from that.
Would I do such a thing? (1)
And in fact establishing a magnetic filed takes energy, but reversing it you get the energy back.
That's how transformers work.
You get *all* the energy back, less the hysteresis losses in the iron core. There are no such losses in the copper windings, and air cored transformers don't suffer them either, they're just not very practical at 50Hz or so due to the size they'd have to be.
To get back to the original consideration of copper or aluminium transmission lines, there are no hysteresis losses in the line. You will get some if the lines are made of ferrous metals, though, but the hysteresis losses would be swamped by the resistive ones.
And because they'd be so enormous, there'd probably be losses in anything for some distance in the form of eddy currents :)
Now cometh a debate re can an ostriches sit on a power line;!()(
What lines are higher then the 400 kV grid then?..
Yep.
Mind you the AL ones are wound on steel cores.
But the resistive losses dominate. Massively.
Because the flux density on a single wire at a few hundred amps only is very very low.
The channel tunnel, that well known airborn structure, eh?
See plenty of birds on 11kV and 33kV lines but I don't think I have ever seen any on the higher voltages. I suppose they must sense the electrical field as they get close.
G.Harman
Apparently ravens and storks like them ...
If your thinking of the bit of video footage I am thinking of, then I have a suspicion that may have been a DC HV line anyway.
Possibly a few stats from A&E departments as well...
Most people who get a shock off the mains without any noticeable effect won't end up in A&E.
Yep. Details below[1][2] for the record + any other sceptical old gits like me ;(
Not to arrive at a third of a million serious injuries. Well the impact assessment in 2013 for the changes to Part P said A&E figures must be treated with caution but the admissions due to electric shock were less than 4,000 a year. That includes non-domestic. It also reminded us that the original Part P assessment estimated "electrical accidents caused around 41 fatalities, 2,740 serious injuries requiring hospital treatment".
____________ [1]Shocks: "4,032 interviews were conducted with adults in Great Britain aged 15+ from 06 to 27 May 2011 via Ipsos MORI's Capibus, the weekly face-to-face omnibus survey, using a nationally representative quota sample across Great Britain. The results have been weighted to reflect the known profile of the adult population in Great Britain. Based on a confidence interval of +/- 0.9% and the sample size of 4,032 the actual number could vary between c2.1 to 2.8 million. Electric shock is defined as 'a mains-voltage electric shock rather than a static shock of the type a person might get from a car, for example."
[2]Injuries: "Based on a survey of 4,032 adults in Great Britain aged 15+ who have personally experienced an electric shock that resulted in injury while at home or in the garden in the past twelve months including all those who experienced one or more of the following injuries: Severe pain, Skin burn without scarring, Bruising from a fall or severe muscular contraction, Temporary blindness, Heartbeat disturbance, Persistent pain or numbness, Higher blood pressure, Skin burn with scarring, Broken bone(s), Difficulty breathing.'"HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.