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Author Topic: Why Does A Tall Power Thing Hum ?  (Read 15474 times)

Offline neilep

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Why Does A Tall Power Thing Hum ?
« on: 01/09/2009 15:32:33 »
Dearest Peeps Of Extraordinary IQ Heights,

As a sheepy I of course luff to humm...humming is my all time favourite sound that one makes as a droany kind of moany mouth closed sound.

But *shock horror*..I is not the only thing that hums !..no no no !!

Near my field is one of these things.



A Humming Thing

I'm convinced that it's a climbing frame for birdies but I've been told that it's holds some magical power and stuff !...woooo !!...

I notice that it also hums !...even more of a wooo !!...why does this power thingy hum ?

As a firm believer in empirical study I snuk into my neighbours house at 3am this morning. Having seen him buy some batteries and knowing that he has hummed a few times...I figure he simply must know about the hummy power thing.So, with a skip and a hop he gleefully put up no resistance as he allowed me to chloroform him again. I luff my neighbour he's great like that, and with him chloroformed up like that he also began to hum and dribble ! So, with his permission to use his car , I backed out of  his garage  and we drove to the power hummy thing. I always wondered how to open his garage doors, it only took three  attempts to reverse through them. So, there we are at 3:30am in the middle of a field ...I tried to wake him but he was so at peace and humming his lullaby that even drenching him in water failed to stir him. I figured, with the help of a winch, If I could just get him to the top of the hummy power thing that the hum would be in concert with his own humming so he could then deliver me the answer. So, I tried one more time to splash him awake and though drenched, I pulled him up to the top till some arcing stuff happened, LOL,,that woke him and I could tell he was happy because he was dancing and iridescent....The foaming at the mouth was a nice touch too..he must have been so enlightened !....though, it made his answer quite unintelligible.....I think he was speaking 'in tongues' !.........so..no luck there !..I left him to these nice people who were jumping over a fire and had something called an altar or something that they were going to make some kind of offering. I told them my neighbour would help as he is always kind like that.

So, can ewe tell me why those power hummy things hum ?...what makes them hum ?


Hugs & Shmishes


mwah mwah mwah !




Neil
HmmmmmmmmmmHmmmmmmmHmmmmmHmmmmm
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
« Last Edit: 01/09/2009 15:34:33 by neilep »


 

Offline RD

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Why Does A Tall Power Thing Hum ?
« Reply #1 on: 01/09/2009 16:24:07 »
Magnetostriction causes steel power lines to hum.
The high alternating current they carry creates an strong alternating magnetic field, which squishes the cable 50/60 times a second, which creates the vibration in the cable which causes the hum, (and its harmonics). 
« Last Edit: 01/09/2009 16:28:20 by RD »
 

Offline LeeE

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Why Does A Tall Power Thing Hum ?
« Reply #2 on: 01/09/2009 16:41:44 »
I thought they hummed because they were in a good mood and feeling happy.
 

Offline Nizzle

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Why Does A Tall Power Thing Hum ?
« Reply #3 on: 02/09/2009 07:44:39 »
So if someone would mess a bit with the switches in the Central distribution, and modulate the AC current through these lines, they could be playing the biggest musical instrument ever?
 

Offline LeeE

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Why Does A Tall Power Thing Hum ?
« Reply #4 on: 02/09/2009 14:35:29 »
That idea really appeals to me  :D
 

Offline neilep

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Why Does A Tall Power Thing Hum ?
« Reply #5 on: 02/09/2009 15:11:11 »
Magnetostriction causes steel power lines to hum.
The high alternating current they carry creates an strong alternating magnetic field, which squishes the cable 50/60 times a second, which creates the vibration in the cable which causes the hum, (and its harmonics). 

Thank ewe very much RD for the info and links....so it literally is the cable itself vibrating !..woo !!
 

Offline neilep

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Why Does A Tall Power Thing Hum ?
« Reply #6 on: 02/09/2009 15:12:29 »
I thought they hummed because they were in a good mood and feeling happy.

Hi LeeE, yes, I am sure they are happy powery hummy things too !...I think if I was one I'd be a happy pylon too !  :)
 

Offline Don_1

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Why Does A Tall Power Thing Hum ?
« Reply #7 on: 02/09/2009 15:13:13 »
Geeze, a vibrator made out of a big Meccano set
 

Offline neilep

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Why Does A Tall Power Thing Hum ?
« Reply #8 on: 02/09/2009 15:15:12 »
So if someone would mess a bit with the switches in the Central distribution, and modulate the AC current through these lines, they could be playing the biggest musical instrument ever?

Now That's a great idea Nizzle...Muzak literally could make the world go round ! ;)
 

Offline neilep

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Why Does A Tall Power Thing Hum ?
« Reply #9 on: 02/09/2009 15:16:02 »
Geeze, a vibrator made out of a big Meccano set

Lol...trust ewe to think of such a thing !......ewe'd need a lot of KY !
 

Offline Don_1

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Why Does A Tall Power Thing Hum ?
« Reply #10 on: 02/09/2009 15:16:45 »
Jelly Jolly good.
 

Offline neilep

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Why Does A Tall Power Thing Hum ?
« Reply #11 on: 02/09/2009 15:54:27 »
Jelly Jolly good.

That's OKY
 

Offline RD

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Why Does A Tall Power Thing Hum ?
« Reply #12 on: 02/09/2009 16:23:36 »
..so it literally is the cable itself vibrating

I think the hum is more audible at the foot of a pylon because sound travels better through solid (metal) than through gas (air).

 (The tin can telephone is an example of this phenomenon). 
 

lyner

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Why Does A Tall Power Thing Hum ?
« Reply #13 on: 02/09/2009 18:23:12 »
I wondered about the magnetic forces between the conductors so I did a fag-packet calculation. With 1000A flowing and a 4m separation (reasonable figures, I think) you get about 0.05N of force per metre for two parallel conductors. (I've ignored the 3 phase thing which could cause all three conductors to do a nice little dance with each other, I guess)
0.05N of force on a 1m length of cable (probably about 5kg(?) would not be expected to produce a lot of oscillation. 10-2m/s/s of average acceleration. However, the whole length (and area) of cable would be moving in phase so, perhaps a low level of sound could be produced that way.
How does that compare, I wonder, with the change in diameter of the conductor produced by Magnetostriction. (Can't be sure of how to do that sum.)

I did wonder, also about the effect of the three phases of currents flowing in the three conductors Would that not tend to reduce the sound level (partial cancellation)? Could the higher level of sound near the towers be something to do with this?
 

Offline Bored chemist

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Why Does A Tall Power Thing Hum ?
« Reply #14 on: 02/09/2009 19:03:40 »
There's also the voltage modulated corona discharge.
If the lines were DC they would hiss- that hiss is modulated at (in the UK) 50 Hz.
 

Offline syhprum

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Why Does A Tall Power Thing Hum ?
« Reply #15 on: 05/09/2009 17:12:19 »
I have often contemplated erecting an antenna wire say 100m long and 2m high beneath 400Kv power lines to see how much power I could siphon off but I have not been brave enough.
It should be quite easy to calculate the power available by anyone skilled in maths, I fear it would be small and the source would be rather high impedance.

PS
1000A at 400KV *6 sounds like an awful lot of power, would not eletrostatic attraction between cables be a larger source of hum (at 50Hz and 150Hz).
« Last Edit: 05/09/2009 17:24:10 by syhprum »
 

Offline Geezer

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Why Does A Tall Power Thing Hum ?
« Reply #16 on: 05/09/2009 17:26:46 »
tell me why those power hummy things hum ?...


Obviously, because they don't know the words. Sheesh...
 

lyner

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Why Does A Tall Power Thing Hum ?
« Reply #17 on: 05/09/2009 17:34:46 »
I have often contemplated erecting an antenna wire say 100m long and 2m high beneath 400Kv power lines to see how much power I could siphon off but I have not been brave enough.
It should be quite easy to calculate the power available by anyone skilled in maths, I fear it would be small and the source would be rather high impedance..

I have a feeling that a lot of iron and a big coil may do better.
 

Offline RD

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Why Does A Tall Power Thing Hum ?
« Reply #18 on: 05/09/2009 18:08:26 »
I have often contemplated erecting an antenna wire say 100m long and 2m high beneath 400Kv power lines to see how much power I could siphon off...



http://vids.myspace.com/index.cfm?fuseaction=vids.individual&videoid=8231948

« Last Edit: 05/09/2009 18:14:38 by RD »
 

Offline that mad man

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Why Does A Tall Power Thing Hum ?
« Reply #19 on: 05/09/2009 19:37:20 »
"I've ignored the 3 phase thing which could cause all three conductors to do a nice little dance with each other, I guess"

You often see (and hear) that dance on the 3 phase cables in lift shafts.
 

Offline Geezer

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Why Does A Tall Power Thing Hum ?
« Reply #20 on: 05/09/2009 19:59:13 »
I have often contemplated erecting an antenna wire say 100m long and 2m high beneath 400Kv power lines to see how much power I could siphon off but I have not been brave enough.
It should be quite easy to calculate the power available by anyone skilled in maths, I fear it would be small and the source would be rather high impedance.

Not too much (power) I suspect. The coupling is not going to be very efficient, but, perhaps more importantly, because your antenna is approximately the same distance from each phase conductor, the magnetic fields will cancel each other out. (This does assume the phase currents are all equal of course, but the power companies do go to a lot of trouble to keep them that way.)

 

Offline syhprum

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Why Does A Tall Power Thing Hum ?
« Reply #21 on: 05/09/2009 20:45:38 »
I was rellying on capacitive coupling between the antenna and the power line, the capacitance between the antenna and the power line and that between the antenna and ground would form a capacitive potential divider with say a division ratio of 10 to 1 giving a voltage on the antenna of 40KV while the output impedance would be 1/2πfc If I knew how to calculate the capacitance of the antenna to ground I could calculate the available power.
With the British system where the 6 conductors are arranged in a ring radiation is reduced it would work better with the continental scheme that has a 2 up and 4 down arrangement and the antenna should be slightly offset.
Due to the long wavelength I think only capacitive effects apply
 

lyner

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Why Does A Tall Power Thing Hum ?
« Reply #22 on: 05/09/2009 23:25:39 »
I was rellying on capacitive coupling between the antenna and the power line, the capacitance between the antenna and the power line and that between the antenna and ground would form a capacitive potential divider with say a division ratio of 10 to 1 giving a voltage on the antenna of 40KV while the output impedance would be 1/2πfc If I knew how to calculate the capacitance of the antenna to ground I could calculate the available power.
With the British system where the 6 conductors are arranged in a ring radiation is reduced it would work better with the continental scheme that has a 2 up and 4 down arrangement and the antenna should be slightly offset.
Due to the long wavelength I think only capacitive effects apply
Unless you were to use an enormous length of cable, the capacitance to earth would be tiny ( not many pF per m) so the source impedance would be very high and, to tune it out (at 50Hz), I think you would need a filthy great inductor. I think that magnetic coupling might be better; it would be easier to get the power out of the circuit. A long, multi-turn coil with its plane vertical and parallel with the conductors with as much iron as you could get could couple better. I'm sure. I estimate about a volt from a 10m high, 100 m loop of wire if there's 1000A flowing but that would be for a single phase system. However - the source impedance would be low enough to allow a lot of amps to flow. Solar heating might be cheaper to instal!
There is the tale of the guy who heated his greenhouses by nicking power from the nearby overhead railway lines. Could be a myth, though.

Is your comment about length and capacity based on antenna theory? That doesn't apply in this case because the source cable  is effectively infinite as the current is uniform over the length and it's not a monopole / dipole. Afaik, the situation is that you effectively have a capacitative potential divider but that you then need to match the power out of it.

Your comment about the  problem with the three  / six cables is certainly right.
« Last Edit: 05/09/2009 23:27:54 by sophiecentaur »
 

Offline Geezer

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Why Does A Tall Power Thing Hum ?
« Reply #23 on: 06/09/2009 01:07:51 »
There is the tale of the guy who heated his greenhouses by nicking power from the nearby overhead railway lines. Could be a myth, though.

That might be a better way to go. Perhaps you could run a long insulated cable close to one of the rails and couple into the return current without going anywhere near the 25kV. Mind you, the current only flows when there is a train in the right relationship, and trains tend to do a lot of coasting, so power might be a bit intermittent.

Course, if you are in the South of England, you could always just tap into the live DC rail directly! (Do not try this at home!)
 

Offline syhprum

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Why Does A Tall Power Thing Hum ?
« Reply #24 on: 06/09/2009 09:45:21 »
750V DC would be a lot safer to tap than 25KV AC, wellington boots and rubber gloves should suffice although switching in a domestic environment might be a bit of a problem due to arcing.
For lighting you could use three lamps in series although you had better hurry up and buy some as filament lamps are to be banned. 
 

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Why Does A Tall Power Thing Hum ?
« Reply #24 on: 06/09/2009 09:45:21 »

 

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