Weird resonance
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Weird resonance

 
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ghiribizzo
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Joined: 22 Nov 2005
Posts: 510
Location: Ferryport-on-Craig. The Kingdom of Fife.

PostPosted: Wed Feb 01, 2006 11:27 pm    Post subject: Weird resonance Reply with quote

Strange occurrance today... foggy/bright sunshine conditions after two days of sub zero temperatures in Fife. The grass, trees etc had a very thick layer of hoar frost/ice on. As I drove towards a point where there were electricity lines - farm type 3 phase - over the road, I was pretty much travelling at right angles to them with the sun directly behind me.
The air was totally still and the wires were resonating at (I guess...) 50Hz. At first I thought the movement of the car was just causing an odd reflection off the lines in the sun but it really was intense bright/dull/bright in the sun. So much so that I stopped and opened the window. Yes, for hundreds of metres this was the case. Never seen it before.
You can tell I used to like the little strange-but-true mags. as a boy! Yes, in Germany I did a detour off-route to make sure I saw the 'Spectre of the Brocken' instead of just the Grey Man... Wink

Anyone else seen the 'flashing' wires? Everyday occurrence at chez H.Nick?
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Wildlifewriter
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Joined: 04 Aug 2005
Posts: 948
Location: Norn Iron

PostPosted: Thu Feb 02, 2006 1:20 am    Post subject: Reply with quote

Interesting. The mechanics of such a thing are way beyond my pay grade - but I doubt that it's anything as simple as a direct 50Hz resonance or flicker.

The human eye cannot detect visual oscillations at that frequency. This is why we don't see a movie as a sequence of projected still images - which it is - and almost all commercial movies are made and shown at a rate of 24 frames per second.

If only we had some qualified physicists or electrical engineers on the forum. Hello.... ?


-Wlw
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HighlandNick
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Joined: 30 Aug 2005
Posts: 635
Location: Highlands, Scotland

PostPosted: Thu Feb 02, 2006 7:53 pm    Post subject: Reply with quote

This phenomenon is called Corona Discharge. The high voltage in overhead cables ionises the air around the cable. This effect is much more noticeable if the lines are dirty or in damp foggy weather. Sometimes you might be able to smell the ionised air as ozone is produced too. In the right conditions, a blueish light can be seen - usually at night. Sea faring folk (come on JA) will know this glow as St Elmos Fire which you can get in highly charged air associated with thunderstorms. Hair raising experiences and glowing ice axes are also reported by mountaineers (come on JA). None of this explains why you should be able to see a rhythmic pulsating though as explained by wlw. Very Happy
Tranmission line engineers sometimes use a special camera that can detect the non visible corona discharge in normal weather conditions that might prelude an insulator breakdown but I believe this is just a plain blueish glow and not a pulsating one.
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ghiribizzo
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Joined: 22 Nov 2005
Posts: 510
Location: Ferryport-on-Craig. The Kingdom of Fife.

PostPosted: Thu Feb 02, 2006 8:02 pm    Post subject: Reply with quote

Hmm. Yes, it is weird. I'm used to seeing discharges in damp weather off automotive spark leads particularly really high voltage CDI types but this was in bright sunlight. It was almost as if someone a few poles away had 'plucked' a line and they were oscillating in a standing wave. All three lines were visibly the same, no birds around that had flown off the lines. I'll need to ask a lineman for the county...
Er, it was very close to where there were crop circles in the autumn. Scully? Mulder?
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Jack Aubrey
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Joined: 31 Aug 2005
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Location: Camptoun, Scotland

PostPosted: Thu Feb 02, 2006 9:11 pm    Post subject: Reply with quote

HighlandNick wrote:
(come on JA)


...if you're physicist or engineer enough??? Ain't neither, I fear. I have watched St Elmo's Fire run around the wingtips of aircraft in a take-off queue at Bangkok while the rain fell like Noah had had fogotten to build. (They don't do "due to late arrival of the incoming aircraft" in that part of the world, do they?!!) And I have had the "tingling ice-axe" experience after topping out on a winter climb in the Mamores. We had coiled ropes and put the axes on our sacks for the descent when the front rolled over and everything went black and buzzy. And "buzzy" does describe it. For a while we (three big, hairy, grown-ups - well as nearly grown-up as chaps get) felt so anxious that we stuck our axes in the snow upslope and waited (here imagine foetal crouches) as the clouds rolled over us. Then we begin to figure that those 6 tools made a very wee target for any ionic discharge, while we three damp figures, even hunkered down, were much more likely to be a zap-point. So we retrieved our ice-tools and as we descended the gully held them in our mitts rather than wearing them aerials. We survived.

Embarrassed Jack
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Seacon
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Joined: 16 Sep 2005
Posts: 56
Location: Northern Ireland

PostPosted: Thu Feb 02, 2006 11:58 pm    Post subject: Reply with quote

Wildlifewriter wrote:


If only we had some qualified physicists or electrical engineers on the forum. Hello.... ?


-Wlw


The phenomenum of Corona Discharge on Overhead Powerlines is quite common particularly in cold and damp atmospheric conditions and is regularly seen by members of the public. Its effect can be increased in coastal regions due to saline build up on overhead line conductors and particularly the supporting insulators.
The resonance of the conductor as described in the original post is strange and is unlikely to be related to the visible Corona Discharge.
The conductor type is likely to be either Steel Cored Aluminium or Hard Drawn Copper. In cold conditions these conductors contract and have greater tension than in warmer temperatures. In addition there is likely to be a stepdown voltage transformer on an adjacent pole. The core of these transformers is constructed of a series of steel plates which are bolted together. The interaction between the steel core and the transformer conductor windings carrying the current creates the change in voltage.

Some transformer cores vibrate due to this magnetic interaction more so than others. This vibration can transfer onto the wood pole and onto the overhead line conductors. I have heard and felt this vibration many times though have never visually seen it. There is a strong possibility that the specific light, atmospheric conditions and viewing angle at the time caused this vibration or resonance to be seen visually.
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ghiribizzo
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Joined: 22 Nov 2005
Posts: 510
Location: Ferryport-on-Craig. The Kingdom of Fife.

PostPosted: Fri Feb 03, 2006 5:13 pm    Post subject: Reply with quote

Seacon wrote:

Some transformer cores vibrate due to this magnetic interaction more so than others. This vibration can transfer onto the wood pole and onto the overhead line conductors. I have heard and felt this vibration many times though have never visually seen it. There is a strong possibility that the specific light, atmospheric conditions and viewing angle at the time caused this vibration or resonance to be seen visually.


I'll go with that! It certainly looked like some form of standing wave was doing it, changing slightly so maybe there was vibration from the transformer at the nearest houses.

Smile
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