[time-nuts] White LED's

Sun Jan 31 15:57:16 UTC 2010

I believe that it is possible to light a fluorescent tube, at least
dimly, by standing on the ground under a power transmission line
operating at more than 100 kV , holding one end of the tube in your
hand, and sticking the other end up in the air.  I have never done
_this_, exactly, but I have held a fluorescent tube near a ham antenna
and seen it light, and on the web I have seen photos of people doing
it under electric utility lines.

Of course I have seen fluorescent tubes light near Van de Graaff
generators and Tesla coils.  We all have.  However, such machines
generate E-fields much stronger than you'll find near ground level
under an electric utility line.

I do _not_ believe that one could get a fluorescent tube to light by
holding it near ground level under an 11-kV line.  But this is just my
gut feeling.  I could certainly be wrong.  I have not done the
experiment; nor have I done a calculation of the expected field
strength.

The story of a farmer drawing enough power "to operate most of his
farm buildings" from a wire running under and parallel to a HV line
sounds like an urban legend to me.  As does the story of a "guy that
had a big coil of wire in the roof of his shed and... could light a
100W incandescent bulb from the stray fields."  It's _hard_ to draw
significant power from the field surrounding a power line because a
huge reactance must be tuned out.  If it were easy, then power-
transmission companies would be dissipating substantial and
economically intolerable amounts of power in the _ground_, which has
non-negligible conductivity.

During my summer working in the engineering department of a Bell
System operating company, I personally observed examples of 60-Hz AC
e.m.f. induced longitudinally in telephone cables running for miles
along rural pole lines, directly under 60-Hz power lines.  It was not
unusual to see an induced e.m.f. of the order of 100 V RMS.  A person
could get a painful shock from this voltage.  However, a human is a
pretty high-resistance load.  You could _not_ draw watts of power from
such a source.  The Thevenin equivalent source impedance was too high.

BTW, it is necessary to distinguish induced e.m.f. from a potential
difference between separated points on the surface of the ground due
to _resistance_ in the ground multiplied by _conduction_ current in
the ground.  Conduction current in the ground arises whenever less
than 100% of the current flowing in a single-phase power line, or the
common-mode current in a three-phase line, does not return through the
neutral wire/cable of the line.  In rural areas where most of the
loads are single-phase, and a three-phase line is tapped for single-
phase loads separated by miles or more, it is not unusual to find very
high ground currents.  I remember observing symptoms of high ground
currents also near electric railroad lines.  As electric locomotive
such as the Pennsylvania RR's GG-1 drew single-phase 25-Hz current
from an overhead wire and returned it through the rails; but a
significant fraction of the return current flowed through the ground,
because the rails were connected to driven "ground" rods, presumably
for safety.  Trolley cars on the streets of Baltimore ran on DC, and
did the same thing.  Some of the ground current would find its way via
safety-ground rods through the neutral wires of the 60-Hz electric
utility.  When this DC flowed through the windings of 60-Hz power
transformers, it partially saturated the transformer cores, causing
waveform distortion, so that 60-Hz harmonics were heard in
neighborhood telephones.

The notion of "ground" as one big equipotential surface, an infinite
sink for charge / current, is a mass delusion.  It's a delusion for DC
and low-frequency AC.  For RF, it is so wrong that words fail me.

-John

> ===============
>
>> I remember hearing about a law suit in an engineering law class I
>> had to
>> take way back when.  It seems a farmer had a long fence running
>> under and
>> parallel to a high tension distribution line.  He had hidden a
>> copper line
>> in it and was harvesting enough power to operate most of his farm
>> buildings.
>> This amounted to a measurable loss from the distribution line and the
>> power
>> company found him out and sued.  The court ruled he had to pay for
>> power
>> used in the past and stop getting his power that way.  Considering
>> the
>> source I don't think this is an urban legend.
>>
>> Regards.
>>
>> Max.  K 4 O D S.
>>
>> Email: max at maxsmusicplace.com
>>
>> Transistor site http://www.funwithtransistors.net
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>>
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>>
>> ----- Original Message -----
>> From: "Chuck Harris" <cfharris at erols.com>
>> To: "Discussion of precise time and frequency measurement"
>> <time-nuts at febo.com>
>> Sent: Saturday, January 30, 2010 12:21 PM
>> Subject: Re: [time-nuts] White LED's
>>
>>
>>> Dr. David Kirkby wrote:
>>>
>>>> I should have added, it carried on glowing for some time after I
>>>> got
>>>> home too. At that point, I was well away from the train lines,
>>>> though
>>>> we
>>>> do have 11 kV overhead cables around 30m from the house. It
>>>> eventually
>>>> stopped glowing so I assume it was the presence of the overhead
>>>> train
>>>> lines which caused this.
>>>
>>> When I was a kid, there was a main set of high tension power lines
>>> several
>>> hundred yards from my house.  I had friends that had garden sheds
>>> under
>>> the
>>> towers that were lit by fluorescent lamps collecting the stray
>>> fields.
>>> A
>>> piece of wire on each end of the bulb enhanced the effect.
>>>
>>> I knew of one guy that had a big coil of wire in the roof of his
>>> shed
>>> and he could light a 100W incandescent bulb from the stray fields.
>>>
>>> -Chuck Harris

> Max Robinson wrote:
>> I remember hearing about a law suit in an engineering law class I had to
>> take way back when.  It seems a farmer had a long fence running under
>> and parallel to a high tension distribution line.  He had hidden a
>> copper line in it and was harvesting enough power to operate most of his
>> farm buildings. This amounted to a measurable loss from the distribution
>> line and the power company found him out and sued.  The court ruled he
>> had to pay for power used in the past and stop getting his power that
>> way.  Considering the source I don't think this is an urban legend.
>>
>> Regards.
>>
>> Max.  K 4 O D S.
>
> It sounds a bit of a myth to me. I've never done the maths, but I doubt
> you
> could get a lot of power from a wire like this. To power most of his farm
> machinery would need many kW.
>
> On the very high power lines, they tend to be location very high, in which
> case
> I would have thought the fields should cancel at long distances, as there
> will
> be 3 out of phase currents.
>
> I think for lighting, you might be able to claim you did it to reduce the
> E-field at your house, as you were worried by the health effects. Sine you
> need
> to dump the power somewhere, a light bulb seemed the cheapest dummy load.
> A 100
> W light bulb is a lot cheaper than a 100 W resistor!
>
> On a similar note, I heard about someone who powered his greenhouse by
> using the
> small voltage between neutral and earth that will exist. I know there is
> at
> least 30 mA available at my house, as shorting neutral to earth will trip
> a 30
> mA RCD. But I measured the voltage once, and whilst I can't recall what it
> was,
>   it was less than 1 Volt.
>
> Dave
>
>
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