Author Topic: Fluorescent Lamps Glow Under XHV Power Lines  (Read 1193 times)
GE101R
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Fluorescent Lamps Glow Under XHV Power Lines « on: October 25, 2019, 03:48:54 PM » Author: GE101R
Many people do not realize this phenomena.

https://youtu.be/cXhZvyGtMrk
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sox35
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Mainly the electrical side of things


missriaelaine
Re: Fluorescent Lamps Glow Under XHV Power Lines « Reply #1 on: October 25, 2019, 04:11:57 PM » Author: sox35
Back in the days when I first got my amateur radio licence, one of our club members, who was a right nutter, had a party piece. He would park in a busy car park just as daylight was fading, and fire up a 100W VHF transmitter. He would then walk nonchalantly around the car carrying a 4ft T12 tube, which of course was glowing brightly from the RF coming from the transmitter.  I'll never know how there was never a multiple car pileup from the traffic going past Cheesy  
« Last Edit: October 25, 2019, 04:15:58 PM by sox35 » Logged

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tolivac
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Re: Fluorescent Lamps Glow Under XHV Power Lines « Reply #2 on: October 25, 2019, 11:45:12 PM » Author: tolivac
One of our 500Kw SW transmitters has an open balun-when it was running at 500Kw-the balun was just outside the building back door.You could hold a U-tube fluorescent bulb out the door and it would light to full brilliance!At another site-an AM and FM site where the FM tower had to be detuned from the AM ones-the FM RF fed to to the tower and FM antenna with an isocoupler-a isolation transformer for RF.You could hold a fluorescent bulb near the hot FM AM end and it lit up the neighborhood children were delighted with my "magic" show.Used the bulb to do some work at the tower bas during the night-AM was off.Onetime th FM antenna got detuned and had high VSWR-you could slide a fluorescent bulb along the line and see the current and voltage points on the line!When the antenna was retuned-no more light shows.
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Medved
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Re: Fluorescent Lamps Glow Under XHV Power Lines « Reply #3 on: November 12, 2019, 03:10:49 PM » Author: Medved
With the power lines: The capacitive current (from the wire to the capacitance formed just by the body size) use to be so high it would be lethal if allowed to flow through the body. Therefore when working on live wires up in the air (close inspection of the wires, their service like spacer replacement or so, usually done at the potential of the wire, insulated from ground), you have to wear shielding metal woven clothing, so the capacitive current has safe way to flow from the point of contact to the whole body surface...
A "standard person" is assumed to form a capacitance of 150pF, e.g. when specifying a model for the human body for electrostatic discharge robustness tests with semiconductors,... And this 150pF at 60Hz and 100kV means already nearly 6mA current, quite a bite when it passes through you...
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Medved
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Re: Fluorescent Lamps Glow Under XHV Power Lines « Reply #4 on: November 20, 2019, 11:33:03 AM » Author: Medved
In other more simplistic words, your body needs to be the same potential as the power line and but that is only on XHV. Bucket trucks, rubber gloves do the job very well at lower primary voltages. When repairing from a helicopter such as replacing or installing spacers, you need only use a rod attached to the aircraft frame and slowly approach the conductor until the potential is reached. Then after the job is completed, you reverse the procedure as you back away from the energized conductors. The only time body "armor" is used in the USA is at 350,000V and above unless the company insists on it.

https://youtu.be/9mcTHQ6xPik


Well, on all voltages above ELV it has to be at the same potential or insulated.
At LV till some low 10's kV work the insulation is the way to go.
The same potential means, there needs to be a current path to actually do the equalization.
With up to 20..30kV, the body capacitance is low enough, so the equalization currents could be tolerated even when going through body. generally the limit uses to be 1mA, what leads to about 15..20kV vs ground, so about 25..35kV between phases.
Above that you do need some shielding (insulating gloves wont help).
The bucket frame (insulated from ground, but connected to the wire) could be good enough for the lower 100's kV (the field is mainly towards ground, so you need the shielding mainly from the bottom anyway), so dedicated body "armor" shielding may not be necessary. Even the harness could serve the same - just a conductive rope hanging parallel to you and connected to the wire could be enough to alter the field so the current through the body gets reduced sufficiently, so in some situations it could be enough as well.

At the XHV you get additional problems in the form of corona discharge, so on top of the field shaping/shielding you should prevent any sharp edges. That means e.g. the rope become unusable (the dangling end would be such unacceptable edge), so then the "armor" (following rather smooth body contours) is not avoidable.


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