Electropherii

[Sub MandrelParticipant @submandrel]

I recall there was a campaign about power lines near schools. I have seen photographs taken at night by the light of a flourescent tube held below a power line (near ground level).

Regardless, I would be interested in any controlled research into any effects.

Neil

[Mark CParticipant @markc]

Re. HV pylons, I heard that the health issues are related to the raised ozone levels that you get but that is never investigated as it is not a direct effect!

Mark

[Sub MandrelParticipant @submandrel]

> I heard that the health issues are related to the raised ozone levels

As in (electric) model railways…

Neil

[jason udallParticipant @jasonudall57142]

It seems (to me) odd that there is “evidence” of health effects under pylons and the like yet no detected/evidence of effect from em fields. . Maybe something else…rain running off ali cables or paint coatings on pylon steel work…have never seen any studies of these other influences… I guess once a cause has been decided then campaigners will look no futher.

[jason udallParticipant @jasonudall57142]

Btw until “recently” water wasn’t magnetic (effected by magnets)

[Bob LambParticipant @boblamb44747]

All this talk about lightning makes me remember a question I have thought about many times. Is a lightning conductor on something like a church spire there to take the full charge of a lightning bolt to earth and not harm the building? Or is it designed to earth any charges that collect at high points on a building by the clouds moving above and make a lightning strike no more likely there as anywhere else? I seem to remember it is not a very good idea to fly a kite in a thunderstorm and I remember having a big earth spike for the winches when I used to go gliding. We also had to stop if there was less than 25 seconds between flash and bang – presumably modern safety requirements now say 25 minutes!

Bob

[jason udallParticipant @jasonudall57142]

Well olevel physics says its to prevent the “build up” of the ground charge matching the cloud charge.. so yes its about prevention….those copper bars wouldn’t pass kind of ( Terra Amps) current in a lightning bolt …well at least not for long

[Bob LambParticipant @boblamb44747]

Thanks Jason – I always thought the bits of copper down the side of a buiding were a bit on the small side to take the massive currents involved – especially if someone has taken the bottom 6 feet off to the scrap man!

[Anonymous]

I suspect that lightning conductors may well protect against a strike, depending upon the size of strike of course. Current flows are high, but not in the tera-amp range. There is an interesting report in this link about a glider struck by lightning, which goes into much detail about lightning strikes.

**LINK**

I have flown in cloud in gliders, but I've never knowingly climbed in a cu-nim. Those I know who have reported getting shocks and sparks off the metal control rods. I've seen what was left of a wooden glider after a lightning strike at the AAIB at Farnborough, and it wasn't much!

I very much doubt that radiation from power lines is a real problem. At 50Hz the wavelength of an EM wave is 6000km. So even a long power line is very short in terms of wavelength. In radiation terms the power line will be electrically short, and electrically short antennas tend to have very low radiation resistance, and are therefore very inefficient radiators. For all practical purposes anybody near a power line will be in the near field, so the field is largely magnetic. The energy in a photon of EM radiation is hf, where h is Planck's constant and f is the frequency. Planck's constant is about 6.63×10^-34, so at 50 Hz not a lot of energy per photon.

Personally I'd be much more concerned about the radiation from a mobile 'phone. The frequency is much higher and the radiation source is an efficient radiator right next to the head. Mind you any problems caused are probably a modern version of natural selection. There's so much verbiage spouted on mobile 'phones I doubt one could tell the difference even if the radiation was having a detrimental effect.

Regards,

Andrew

[Billy MillsParticipant @billymills]

If Building structures get wet then hit by lightening the water converts to steam and does a lot of damage to the building. The current in the average strike is around 25,000 A for a few uS, it is NOT Terra Amps but the strike is very complex, no two the same. The peak current has been indicated by the intensity of magnitisation of soft iron rods placed near the conductor as well as other methods.

Lightning conductors are aimed at giving the strike an easier path to ground than through the structure to minimise damage, very many buildings are saved by lightning conductors every year. Some buildings get hit very frequently, but for every strike to ground there are roughly three times as many cloud to cloud.

After taking a strike it is a good idea to check the conductor's condition! a six foot gap is not a great big issue for lightning that has traveled several miles but it is not good for people nearby. Sometimes the conductor can break free of some of the cleats and gets stretched into a bow shape said to be caused by the local magnetic field – not quite the same as welder cable twitch!.

Billy.

[Anonymous]

Posted by Billy Mills on 01/08/2013 12:08:38:

If Building structures get wet then hit by lightening the water converts to steam……..

…..which is precisely what happened to the wooden glider. The water in the spar turned to steam and the spar structure literally exploded. What was left was a 'mush' and fused steel control cables.

Regards,

Andrew

[Gordon WParticipant @gordonw]

When I was A boy, we were sheltering from the storm under a big tree, being good boy scouts decided this was not a good idea so ran for the hedge. A very big bang made us stop, where we had been was now a large hole, so a bit wary now. Have been climbing into a storm, the feeling when all the hair on your body stands on end is unforgetable. Guess must be similar in a glider.

[Billy MillsParticipant @billymills]

There was an article in Electronics and Wireless World many years ago called " Killing Fields" which was about the fields near HV transmission lines. There is some evidence for magnetic fields having a biological effect however these effects vary greatly with different people. It is certainly true that ozone is very dangerous to some people in very small concentrations however transmission lines are high in the air and wind flow speeds are a lot higher than at ground level. So there are a few complicating factors.

The normal -fine weather-electric field is around 600V from head to toes ( if you are standing up) so we all get exposed to quite high electric fields when outside.

Like Gordon, I was outdoors in a Storm once, there was a near strike- total sensory overload and glad to be alive feelings as the eardrums recovered. But would not like to be in a glider blown out of the sky. Will stick to flying in Faraday cages. Wood is around 10% wet when seasoned under cover so there is plenty of steam volume available.

Billy.

[Sub MandrelParticipant @submandrel]

As I recall, a pointed conductor concentrates charge at the end and creates a stream of charged particles. Lightning rods therefore create a 'cloud' of charge above them which might reduce the severity of a strike.

The wikipedia article on lightning rods seems to cover many possible modes of operation, but seems to be short on hard facts.

Neil

[V8EngParticipant @v8eng]

I observed the indirect power of lightning last week:

There was a storm rumbling round the area, then Flash of lightning with a simultaneous clap of thunder and the house seemed to fill with light, my Broadband Router stopped working (never to go again), my CCTV recorder lost 3 channels plus I am unable to accesss its settings now

Fortunately we were not actually hit directly and I could not detect any other damage.

That was a couple of hundred pounds lost in an instant, costly business these natural generating systems!

Edited By V8Eng on 02/08/2013 21:18:40

[Ian PParticipant @ianp]

When I were but a lad, I worked for a few years in radio & TV repair. One house I went to must have had a lightning strike that required a repair to the TV which I did in the workshop. When the TV was returned to the customer the engineer found that there was no signal from the aerial although the aerial looked OK from the street and was plugged in to the TV. The engineer diligently checked with his meter that the coax was not shorted but he took the cover off the plug and then discovered why there was no signal.

The coaxial downlead consisted of two concentric plastic tubes! Not a trace of copper in the yard or so he stripped back, just the odd darkened area of polythene and If I remember correctly a few slits in the outer sleeve where the vapourised copper must have escaped.

Ian P

[Sam StonesParticipant @samstones42903]

Martin,

You whizzed me back to early ‘57 and the time when we bods were training to be ground wireless mechanics at RAF Locking.

We had to gain an understanding of CRDF by drawing the block diagram, and also climbing onto the roof to get a glimpse of the four-way dipole and the triode valve with its special `grounded’ grid.

Happy daze!

Sam

[Gordon WParticipant @gordonw]

Talking about these things in the pub last night ( where else ) I was recalling a " ball lightening " attack when I was a kid, seen it once or twice since, but never heard of now. Does modern equipment stop these happenings, or is it just nobody notices ?

[jason udallParticipant @jasonudall57142]

http://www.google.co.uk/url?sa=t&source=web&cd=2&ved=0CC4QFjAB&url=http%3A%2F%2Fhome.planet.nl%2F~icblsec%2F1995.html&ei=GZD9UYSRCYHy7Abxi4GADA&usg=AFQjCNEJ4dx2Z4XPFnZD96QBbZDc3LcLpw&sig2=HI19TznkzYVYlxj_PLYiWQ

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

(1) Producing very high voltages has been a quest of engineers and scientists for many years . Initially there were just friction type electrostatic generators which could produce high voltages but more sophisticated machines rapidly came along .

Some of these are :

Whimshurst machine

Van der Graf generator

Induction coil

High voltage transformers (and Tesla coils)

High voltage dynamo

Switched capacitor bank

Van der Graf generators were very successful and being easy to make there have been many built all over the world – some of large size and power .

Favoured method these days is the switched capacitor bank . There is a research facility that can concentrate all the discharge power of an enormous switched capacitor bank into a tiny work cell .

(2) At a more mundane level we once had a radio with a trembler to produce the valve HT – ordinary mains hum would now seem a luxury by comparison !!

MikeW

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