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| Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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Lightning protection
Hi folks...this was in a baseball newsgroup that I participate in (rec.sport.baseball). Faraday cages have been mentioned, implying that it could be safe. I don't know that I'd trust this against lightning (maybe a Van de Graff generator). What do you think? "Just wondering if sitting on a wood bench inside a metal cage (i.e. metal on top and 4 sides) is a safe place to be during a lightning storm. This is similar to the situation of being in a car (except for the rubber tires!). I have seen younger kids wait out a passing storm this way and am wondering if it IS in fact safe? What would the effect of metal cleats be? I'd appreciate any thoughts from anybody but especially from physics teachers/physicists. Thanks!" Tom |
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#2
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"Tom MacIntyre" wrote in message ... Hi folks...this was in a baseball newsgroup that I participate in (rec.sport.baseball). Faraday cages have been mentioned, implying that it could be safe. I don't know that I'd trust this against lightning (maybe a Van de Graff generator). What do you think? "Just wondering if sitting on a wood bench inside a metal cage (i.e. metal on top and 4 sides) is a safe place to be during a lightning storm. This is similar to the situation of being in a car (except for the rubber tires!). I have seen younger kids wait out a passing storm this way and am wondering if it IS in fact safe? What would the effect of metal cleats be? I'd appreciate any thoughts from anybody but especially from physics teachers/physicists. Thanks!" Tom there is no guarantee that a baseball cage is adequately grounded. the support poles are usually set in concrete. faraday cages are meant to block RF. lightning is DC (mostly). refer to http://www.lightningsafety.com/nlsi_pls/lst.html http://www.securityworld.com/communi...ingsafety.html http://www.nhoem.state.nh.us/mitigation/fig%203-16.htm http://www.metlife.com/Applications/...,P4091,00.html http://www.scouter.com/compass/Leade...htning_Safety/ i routinely repair lightning damaged equipment. when you see first hand large molten globs of metal, ceramic, and other material that used to be perfectly good electronics you tend to get real cautious about where you go and what you do when a lightning storm passes through. |
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#3
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Effectiveness of protection from lightning is determined by how that
electricity gets to earth ground. Not earth ground beneath you. If seeks charges via earth that is maybe miles away. In the process, the struck batting cage then carries electricity underneath your feet to to take a mile plus path to those distant charges. For example, if standing on earth with feet apart, and if the nearby tree is struck, then electricity might pass through earth, up one leg, down the other, and then continue through earth. Therefore the human is electrocuted. This is also why four legged animals tend to be at risk when a nearby tree is struck. Four legged animals do not make a single point ground connection to earth; therefore can be harmed by electricity flowing through the earth. The baseball cage may act as a good lightning rod. But then electricity passes beneath a human to cause harm. IOW the faraday cage is not complete because the earth beneath the human was not sufficiently conductive. BTW, lightning is not DC. Lightning is AC current - mostly in radio frequency ranges. This AC nature is why longer conductors, sufficient for 60 Hz AC electric power, can be poor conductors to lightning; its energy in higher frequencies. This AC nature of lightning is why so many humans think lightning is capricious. Tom MacIntyre wrote: Hi folks...this was in a baseball newsgroup that I participate in (rec.sport.baseball). Faraday cages have been mentioned, implying that it could be safe. I don't know that I'd trust this against lightning (maybe a Van de Graff generator). What do you think? |
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#4
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Effectiveness of protection from lightning is determined by how that
electricity gets to earth ground. Not earth ground beneath you. If seeks charges via earth that is maybe miles away. In the process, the struck batting cage then carries electricity underneath your feet to to take a mile plus path to those distant charges. For example, if standing on earth with feet apart, and if the nearby tree is struck, then electricity might pass through earth, up one leg, down the other, and then continue through earth. Therefore the human is electrocuted. This is also why four legged animals tend to be at risk when a nearby tree is struck. Four legged animals do not make a single point ground connection to earth; therefore can be harmed by electricity flowing through the earth. The baseball cage may act as a good lightning rod. But then electricity passes beneath a human to cause harm. IOW the faraday cage is not complete because the earth beneath the human was not sufficiently conductive. BTW, lightning is not DC. Lightning is AC current - mostly in radio frequency ranges. This AC nature is why longer conductors, sufficient for 60 Hz AC electric power, can be poor conductors to lightning; its energy in higher frequencies. This AC nature of lightning is why so many humans think lightning is capricious. Tom MacIntyre wrote: Hi folks...this was in a baseball newsgroup that I participate in (rec.sport.baseball). Faraday cages have been mentioned, implying that it could be safe. I don't know that I'd trust this against lightning (maybe a Van de Graff generator). What do you think? |
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#5
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"TimPerry" wrote in message ... i routinely repair lightning damaged equipment. when you see first hand large molten globs of metal, ceramic, and other material that used to be perfectly good electronics you tend to get real cautious about where you go and what you do when a lightning storm passes through. Yep, you never know. I hide under the bed myself. N |
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BTW, lightning is not DC. Lightning is AC current - mostly in radio
frequency ranges. This AC nature is why longer conductors, sufficient for 60 Hz AC electric power, can be poor conductors to lightning; its energy in higher frequencies. This AC nature of lightning is why so many humans think lightning is capricious. utter and complete crap. lightning is an electrostatic discharge. |
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#7
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"w_tom" wrote in message
oups.com... Effectiveness of protection from lightning is determined by how that electricity gets to earth ground. Not earth ground beneath you. If seeks charges via earth that is maybe miles away. In the process, the struck batting cage then carries electricity underneath your feet to to take a mile plus path to those distant charges. For example, if standing on earth with feet apart, and if the nearby tree is struck, then electricity might pass through earth, up one leg, down the other, and then continue through earth. Therefore the human is electrocuted. This is also why four legged animals tend to be at risk when a nearby tree is struck. Four legged animals do not make a single point ground connection to earth; therefore can be harmed by electricity flowing through the earth. The baseball cage may act as a good lightning rod. But then electricity passes beneath a human to cause harm. IOW the faraday cage is not complete because the earth beneath the human was not sufficiently conductive. BTW, lightning is not DC. Lightning is AC current - mostly in radio frequency ranges. This AC nature is why longer conductors, sufficient for 60 Hz AC electric power, can be poor conductors to lightning; its energy in higher frequencies. This AC nature of lightning is why so many humans think lightning is capricious. Tom MacIntyre wrote: Hi folks...this was in a baseball newsgroup that I participate in (rec.sport.baseball). Faraday cages have been mentioned, implying that it could be safe. I don't know that I'd trust this against lightning (maybe a Van de Graff generator). What do you think? Lightning is AC ?!!!. I've never seen any rotating clouds, in the UK we get plenty of lighning but no rotating tornados with lightning. -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
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#8
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w_tom wrote:
The baseball cage may act as a good lightning rod. But then electricity passes beneath a human to cause harm. IOW the faraday cage is not complete because the earth beneath the human was not sufficiently conductive. With no mesh underfoot, it might depend on the shape of the cage. If you were surrounded on three sides, there might not be much current underfoot because the metal fence would be a better conductor. At the nearest playground, the "batter's cage" is just a wide V backstop, so I wouldn't stand there in a storm. Pointy rods on the top of the cage might prevent a lot of strikes by bleeding off charges. BTW, lightning is not DC. Lightning is AC current - mostly in radio frequency ranges. This AC nature is why longer conductors, sufficient for 60 Hz AC electric power, can be poor conductors to lightning; its energy in higher frequencies. This AC nature of lightning is why so many humans think lightning is capricious. I think I've read that there can be several phases in a lightning strike, and maybe electricity flows back and forth. I can't remember. Anyway, lightning doesn't have to be AC for a power line to be a poor conductor. Inductance reacts against a sudden change in current. With lightning, the change is so sudden that a little inductance means a lot of impedance. Leading from a 220V transformer to a house, the three conductors are usually twisted together nowadays. The reduces inductance. I'll bet we'd have less damage from surges with fast rise times, whether or not caused by lightning, if power companies spaced the conductors a foot apart as they once did. |
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#9
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w_tom wrote:
snip BTW, lightning is not DC. Lightning is AC current - mostly in radio frequency ranges. This AC nature is why longer conductors, sufficient for 60 Hz AC electric power, can be poor conductors to lightning; its energy in higher frequencies. This AC nature of lightning is why so many humans think lightning is capricious. Huh? Cite? snip - The e-mail address in our reply-to line is reversed in an attempt to minimize spam. Our true address is of the form . |
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#10
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To make it easier for some to understand, I should have first noted
that lightning is an impulse. The classic current transient is an 8/20 microsecond impulse. That impulse is a summation of frequency components; AC waveforms at various radio frequencies. This is basic knowledge to those with electrical engineering training AND those with math backgrounds that include Fourier Series. Lightning obviously is not DC. If it was, then only wire resistance would be relevant. An impulse due to lightning contains numeorus AC sine waves. Much of that energy is in the 100 kilohertz and Megahertz range. These obviously are not DC. Wire resistance has very little relevance. Wire impedance is a dominant parameter due to sine waves in an 8/20 usec impulse called CG lightning. Wire impedance would be completely irrelevant if lightning were DC. Nothing new about this. First year electrical engineers even study impulse response. Those who have a problem with this concept will have difficulty understanding the electrical nature of lightning. Clearly lightning is not DC because lightning current is an impulse in the microsecond range. CJT wrote: w_tom wrote: BTW, lightning is not DC. Lightning is AC current - mostly in radio frequency ranges. This AC nature is why longer conductors, sufficient for 60 Hz AC electric power, can be poor conductors to lightning; its energy in higher frequencies. This AC nature of lightning is why so many humans think lightning is capricious. Huh? Cite? |
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#11
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To all:
This statement is correct. A lightning bolt often consists of as many as 40 to 50 individual discharges. This is not apparent unless the lightning is captured by high speed photography. So, since the lightning discharge turns on and off 40 to 50 times in a fraction of a second, it is not pure DC. The current flows in only one direction. However, the energy is split between a DC component, and a considerable part that is effectively RF energy. Note this is RF energy, not low frequency AC. I don't have a Web source to cite for this, but I have read about this before. Specifically, that a ground for a lightning rod must not go through a coil of wire. Aidan Grey On 5 Jul 2005 06:40:58 -0700, w_tom wrote: Effectiveness of protection from lightning is determined by how that electricity gets to earth ground. Not earth ground beneath you. If seeks charges via earth that is maybe miles away. In the process, the struck batting cage then carries electricity underneath your feet to to take a mile plus path to those distant charges. For example, if standing on earth with feet apart, and if the nearby tree is struck, then electricity might pass through earth, up one leg, down the other, and then continue through earth. Therefore the human is electrocuted. This is also why four legged animals tend to be at risk when a nearby tree is struck. Four legged animals do not make a single point ground connection to earth; therefore can be harmed by electricity flowing through the earth. The baseball cage may act as a good lightning rod. But then electricity passes beneath a human to cause harm. IOW the faraday cage is not complete because the earth beneath the human was not sufficiently conductive. BTW, lightning is not DC. Lightning is AC current - mostly in radio frequency ranges. This AC nature is why longer conductors, sufficient for 60 Hz AC electric power, can be poor conductors to lightning; its energy in higher frequencies. This AC nature of lightning is why so many humans think lightning is capricious. Tom MacIntyre wrote: Hi folks...this was in a baseball newsgroup that I participate in (rec.sport.baseball). Faraday cages have been mentioned, implying that it could be safe. I don't know that I'd trust this against lightning (maybe a Van de Graff generator). What do you think? |
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#12
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"Aidan Grey" wrote in message
k.com... To all: This statement is correct. A lightning bolt often consists of as many as 40 to 50 individual discharges. This is not apparent unless the lightning is captured by high speed photography. So, since the lightning discharge turns on and off 40 to 50 times in a fraction of a second, it is not pure DC. The current flows in only one direction. However, the energy is split between a DC component, and a considerable part that is effectively RF energy. Note this is RF energy, not low frequency AC. I don't have a Web source to cite for this, but I have read about this before. Specifically, that a ground for a lightning rod must not go through a coil of wire. Aidan Grey On 5 Jul 2005 06:40:58 -0700, w_tom wrote: Effectiveness of protection from lightning is determined by how that electricity gets to earth ground. Not earth ground beneath you. If seeks charges via earth that is maybe miles away. In the process, the struck batting cage then carries electricity underneath your feet to to take a mile plus path to those distant charges. For example, if standing on earth with feet apart, and if the nearby tree is struck, then electricity might pass through earth, up one leg, down the other, and then continue through earth. Therefore the human is electrocuted. This is also why four legged animals tend to be at risk when a nearby tree is struck. Four legged animals do not make a single point ground connection to earth; therefore can be harmed by electricity flowing through the earth. The baseball cage may act as a good lightning rod. But then electricity passes beneath a human to cause harm. IOW the faraday cage is not complete because the earth beneath the human was not sufficiently conductive. BTW, lightning is not DC. Lightning is AC current - mostly in radio frequency ranges. This AC nature is why longer conductors, sufficient for 60 Hz AC electric power, can be poor conductors to lightning; its energy in higher frequencies. This AC nature of lightning is why so many humans think lightning is capricious. Tom MacIntyre wrote: Hi folks...this was in a baseball newsgroup that I participate in (rec.sport.baseball). Faraday cages have been mentioned, implying that it could be safe. I don't know that I'd trust this against lightning (maybe a Van de Graff generator). What do you think? chopped DC makes sense - anyone know what initiates the chopping and the rate of chop? Is chopped DC the discharge mechanism from van de graff's etc? |
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#13
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Aidan Grey wrote:
To all: This statement is correct. A lightning bolt often consists of as many as 40 to 50 individual discharges. This is not apparent unless the lightning is captured by high speed photography. So, since the lightning discharge turns on and off 40 to 50 times in a fraction of a second, it is not pure DC. The current flows in only one direction. However, the energy is split between a DC component, and a considerable part that is effectively RF energy. Note this is RF energy, not low frequency AC. A small multiple of 40-50 Hz is not exactly RF. So what's the risetime of these pulses? Duration? I don't have a Web source to cite for this, but I have read about this before. Specifically, that a ground for a lightning rod must not go through a coil of wire. Why would you want one to run through a coil, anyway? I suspect the warning is to avoid somebody being electrocuted by induced current from the pulse(s). Aidan Grey On 5 Jul 2005 06:40:58 -0700, w_tom wrote: Effectiveness of protection from lightning is determined by how that electricity gets to earth ground. Not earth ground beneath you. If seeks charges via earth that is maybe miles away. In the process, the struck batting cage then carries electricity underneath your feet to to take a mile plus path to those distant charges. For example, if standing on earth with feet apart, and if the nearby tree is struck, then electricity might pass through earth, up one leg, down the other, and then continue through earth. Therefore the human is electrocuted. This is also why four legged animals tend to be at risk when a nearby tree is struck. Four legged animals do not make a single point ground connection to earth; therefore can be harmed by electricity flowing through the earth. The baseball cage may act as a good lightning rod. But then electricity passes beneath a human to cause harm. IOW the faraday cage is not complete because the earth beneath the human was not sufficiently conductive. BTW, lightning is not DC. Lightning is AC current - mostly in radio frequency ranges. This AC nature is why longer conductors, sufficient for 60 Hz AC electric power, can be poor conductors to lightning; its energy in higher frequencies. This AC nature of lightning is why so many humans think lightning is capricious. Tom MacIntyre wrote: Hi folks...this was in a baseball newsgroup that I participate in (rec.sport.baseball). Faraday cages have been mentioned, implying that it could be safe. I don't know that I'd trust this against lightning (maybe a Van de Graff generator). What do you think? -- The e-mail address in our reply-to line is reversed in an attempt to minimize spam. Our true address is of the form . |
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#14
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Risetime of these current pulses was provided in a previous
post: exponentially rising and falling edges of 8/20 microseconds. Obviously the ground wire would not be run through a coil. But due to the high frequency nature of transients, that ground wire must not be spliced, no sharp bends, and not routed inside metallic materials. A violation would only increase wire impedance unacceptably. Why? Because even sharp bends cause significant impedance increases when discussing the higher frequency components of lightning. We could play a game of 50,000 questions since even the most basic nature of lightning - its RF components - is new information. These and other questions have been answered previously in a list of citations at: http://makeashorterlink.com/?X61C23DCA Figure about one days worth of reading. CJT wrote: A small multiple of 40-50 Hz is not exactly RF. So what's the risetime of these pulses? Duration? ... Why would you want one to run through a coil, anyway? I suspect the warning is to avoid somebody being electrocuted by induced current from the pulse(s). |
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#15
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"w_tom" wrote in message ... Risetime of these current pulses was provided in a previous post: exponentially rising and falling edges of 8/20 microseconds. Obviously the ground wire would not be run through a coil. But due to the high frequency nature of transients, that ground wire must not be spliced, no sharp bends, and not routed inside metallic materials. A violation would only increase wire impedance unacceptably. Why? Because even sharp bends cause significant impedance increases when discussing the higher frequency components of lightning. We could play a game of 50,000 questions since even the most basic nature of lightning - its RF components - is new information. These and other questions have been answered previously in a list of citations at: http://makeashorterlink.com/?X61C23DCA citing a newsgroup discussion is not a valid reference. elaborate (and probably inaccurate) discussion as to the exact nature of lightning will not be of benefit to the original poster. a DC pulse is still a DC pulse no amount of wishful thinking will turn it in to AC (granted that there are some aspects that generate RF and perhaps some other characteristics that may be able to be handled by AC analysis) looking at a few of toms 16,900 archived posts i see he also claims that a ground rod in rock will make a perfectly good ground. from that it follows that a batting cage set in concrete is adiquitly grounded. i dont think so. Figure about one days worth of reading. CJT wrote: A small multiple of 40-50 Hz is not exactly RF. So what's the risetime of these pulses? Duration? ... Why would you want one to run through a coil, anyway? I suspect the warning is to avoid somebody being electrocuted by induced current from the pulse(s). |
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#16
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w_tom wrote:
To make it easier for some to understand, I should have first noted that lightning is an impulse. The classic current transient is an 8/20 microsecond impulse. That impulse is a summation of frequency components; AC waveforms at various radio frequencies. This is basic knowledge to those with electrical engineering training AND those with math backgrounds that include Fourier Series. Lightning obviously is not DC. If it was, then only wire resistance would be relevant. An impulse due to lightning contains numeorus AC sine waves. That a pulse is susceptible to Fourier analysis does not make it "contain numerous AC sine waves." Much of that energy is in the 100 kilohertz and Megahertz range. These obviously are not DC. Wire resistance has very little relevance. Wire impedance is a dominant parameter due to sine waves in an 8/20 usec impulse called CG lightning. Wire impedance would be completely irrelevant if lightning were DC. Nothing new about this. First year electrical engineers even study impulse response. Those who have a problem with this concept will have difficulty understanding the electrical nature of lightning. Clearly lightning is not DC because lightning current is an impulse in the microsecond range. CJT wrote: w_tom wrote: BTW, lightning is not DC. Lightning is AC current - mostly in radio frequency ranges. This AC nature is why longer conductors, sufficient for 60 Hz AC electric power, can be poor conductors to lightning; its energy in higher frequencies. This AC nature of lightning is why so many humans think lightning is capricious. Huh? Cite? -- The e-mail address in our reply-to line is reversed in an attempt to minimize spam. Our true address is of the form . |
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#17
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w_tom wrote:
Risetime of these current pulses was provided in a previous post: exponentially rising and falling edges of 8/20 microseconds. I took what you wrote previously to be the pulse duration, not its risetime. Obviously the ground wire would not be run through a coil. But due to the high frequency nature of transients, that ground wire must not be spliced, no sharp bends, and not routed inside metallic materials. A violation would only increase wire impedance unacceptably. Why? Because even sharp bends cause significant impedance increases when discussing the higher frequency components of lightning. An 8 microsecond risetime doesn't imply all that high a frequency. Sharp bends in thick wire at ultrasonic frequencies aren't a big deal. We could play a game of 50,000 questions since even the most basic nature of lightning - its RF components - is new information. These and other questions have been answered previously in a list of citations at: http://makeashorterlink.com/?X61C23DCA Figure about one days worth of reading. CJT wrote: A small multiple of 40-50 Hz is not exactly RF. So what's the risetime of these pulses? Duration? ... Why would you want one to run through a coil, anyway? I suspect the warning is to avoid somebody being electrocuted by induced current from the pulse(s). -- The e-mail address in our reply-to line is reversed in an attempt to minimize spam. Our true address is of the form . |
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#18
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You are joking. Right? The Fourier analysis of lightning
reveals energy at numerous frequencies. Lightning is RF electricity. That RF energy is why lightning even causes noise on radios. So now you say all those RF sine waves, demonstrated by Fourier analysis, really do not exist? Why not just say the world is still flat? If lightning did not have so much energy in RF, then radios would not receive that RF noise. An example that demonstrates the RF nature of pulses and of lightning. Pulses are not DC. If lightning were DC, then wire impedance would not be relevant. But lets put numbers to it. A 50 foot 20 amp wire may be 0.2 ohms resistance. But wire reactance means same wire has something like 120 ohms impedance to a lightning transient. Why is impedance so much larger than the resistance? Because the RF components of lightning make impedance relevant and significant. If lighting were DC, then wire resistance and wire impedance would be same. If lightning were DC, then lightning would not have such destructive consequences. Fourier analysis demonstrates lightning is AC electricity at many frequencies. Putting a number to the impulse - 8/20 microseconds - explains why so much energy is in the Megahertz range. Using DC analysis to explain lightning means that person never first learned basic transient analysis taught to first year EE students. Lightning has massive energy in radio frequencies which makes lightning so uniquely destructive. Those radio frequencies even mean that an earthing wire bundled with other wires will induce transients on those other wires. DC electricity would not do that inducing. Why are induced transients a problem with lightning? Because lighting is AC electricity - as demonstrated by Fourier analysis, as demonstrated by discussion about impedance, as demonstrated by what first year EE students are taught, as demonstrated by noise on the radio, and as demonstrated by so many industry professional cited in: http://makeashorterlink.com/?X61C23DCA Show me. Show me how lightning is only DC. Provide supporting facts. Provide industry citations as I have done repeatedly. Declaring something without supporting facts is classic junk science reasoning. Where are those supporting facts, the numbers, and industry professional citations that declare lightning as DC electricity? Without supporting facts, et al, then your claim is really nothing more than personal speculation or urban myth. Show me. Provide facts and numbers. Provide the underlying math. Show me that capacitors and inductors are irrelevant to conducting lightning's DC electricity. Show me rather than make unsubstantiated claims. Show me how you know that lightning is DC electricity. Show me that you also know the difference between ultrasonics and electricity. CJT wrote: That a pulse is susceptible to Fourier analysis does not make it "contain numerous AC sine waves." |
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#19
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Point one. Deny citations from industry professionals by
refusing to read them. An ostrich does that; not an informed human. Cited are numerous technical papers and other technical facts on lightning - literally a full days worth of reading. Instead TimPerry pretends those citations did not exist in: http://makeashorterlink.com/?X61C23DCA A DC pulse is an oxymoron. As confusing as another ridiculous term: DC triangle wave. Either it is a pulse affected by reactance (inductors and capacitors), or it is only DC that completely ignores reactance. One cannot have it both ways. Either it is DC that ignores reactance, or it is a pulse that makes reactance relevant. Which is it? If lightning is DC, then inductance, capacitance, and impedance is not discussed. Why do industry professionals discuss these repeatedly? Because lightning is not DC. Pulses are transient responses - taught in 1st year engineering - an introduction to AC characteristics. AC analysis makes wire inductance and capacitance significant. DC analysis ignores inductance and capacitance. To understand how lightning works - as cited in http://makeashorterlink.com/?X61C23DCA - one cannot pretend lightning is DC. A lightning impulse is an AC or transient event. Lightning is a composition of many frequencies. Show me a DC wave that has frequency components? You cannot. That is the oxymoron of DC pulse. A 'pulse' has AC components. 'DC' has no AC components. Oxymoron. Equally confusing is to say "DC triangle wave". DC pulse or DC triangle wave - both are oxymorons. Both contain numerous frequency components. Therefore a 'DC pulse' cannot be analyzed using DC analysis. Lightning requires AC analysis. Lightning is not a DC event. Point two. TimPerry believes a batting cage set in concrete is not conductive. TimPerry should first read those discussions he refused to learn from in: http://makeashorterlink.com/?X61C23DCA A most superior earth ground is an Ufer ground. Why? The earthing is through concrete. Had TimPerry first learned what industry professionals teach, then he would have known the batting cage mounted in concrete makes a best earthing ground - exactly like Ufer grounds. But then TimPerry also promotes an oxymoron called 'DC pulse'. Somehow he knows without first learning the facts. If only he had first read those citations and first learned about Ufer grounding. Then he would not have posted, "i dont think so." One should first learn before knowing something. The energy of lightning is AC electricity. TimPerry wrote: citing a newsgroup discussion is not a valid reference. elaborate (and probably inaccurate) discussion as to the exact nature of lightning will not be of benefit to the original poster. a DC pulse is still a DC pulse no amount of wishful thinking will turn it in to AC (granted that there are some aspects that generate RF and perhaps some other characteristics that may be able to be handled by AC analysis) looking at a few of toms 16,900 archived posts i see he also claims that a ground rod in rock will make a perfectly good ground. from that it follows that a batting cage set in concrete is adiquitly grounded. i dont think so. |
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#20
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w_tom wrote:
You are joking. Right? The Fourier analysis of lightning reveals energy at numerous frequencies. Lightning is RF electricity. That RF energy is why lightning even causes noise on radios. So now you say all those RF sine waves, demonstrated by Fourier analysis, really do not exist? Why not just say the world is still flat? If lightning did not have so much energy in RF, then radios would not receive that RF noise. An example that demonstrates the RF nature of pulses and of lightning. Pulses are not DC. If lightning were DC, then wire impedance would not be relevant. But lets put numbers to it. A 50 foot 20 amp wire may be 0.2 ohms resistance. But wire reactance means same wire has something like 120 ohms impedance to a lightning transient. Why is impedance so much larger than the resistance? Because the RF components of lightning make impedance relevant and significant. If lighting were DC, then wire resistance and wire impedance would be same. If lightning were DC, then lightning would not have such destructive consequences. Fourier analysis demonstrates lightning is AC electricity at many frequencies. Putting a number to the impulse - 8/20 microseconds - explains why so much energy is in the Megahertz range. Using DC analysis to explain lightning means that person never first learned basic transient analysis taught to first year EE students. Lightning has massive energy in radio frequencies which makes lightning so uniquely destructive. Those radio frequencies even mean that an earthing wire bundled with other wires will induce transients on those other wires. DC electricity would not do that inducing. Why are induced transients a problem with lightning? Because lighting is AC electricity - as demonstrated by Fourier analysis, as demonstrated by discussion about impedance, as demonstrated by what first year EE students are taught, as demonstrated by noise on the radio, and as demonstrated by so many industry professional cited in: http://makeashorterlink.com/?X61C23DCA Show me. Show me how lightning is only DC. Provide supporting facts. Provide industry citations as I have done repeatedly. Declaring something without supporting facts is classic junk science reasoning. Where are those supporting facts, the numbers, and industry professional citations that declare lightning as DC electricity? Without supporting facts, et al, then your claim is really nothing more than personal speculation or urban myth. Show me. Provide facts and numbers. Provide the underlying math. Show me that capacitors and inductors are irrelevant to conducting lightning's DC electricity. Show me rather than make unsubstantiated claims. Show me how you know that lightning is DC electricity. Show me that you also know the difference between ultrasonics and electricity. CJT wrote: That a pulse is susceptible to Fourier analysis does not make it "contain numerous AC sine waves." well I'd never even thought about whether it was AC DC or whatever. But its an interesting discussion... Its certainly disruptive across a wide band of the rf spectrum. I wouldn't make a phone call if it was overhead anyway! hmmm |
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#21
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w_tom wrote:
You are joking. Right? The Fourier analysis of lightning reveals energy at numerous frequencies. Lightning is RF electricity. That RF energy is why lightning even causes noise on radios. So now you say all those RF sine waves, demonstrated by Fourier analysis, really do not exist? You're demonstrating a basic lack of understanding of Fourier analysis. Fourier used the sine function as a basis function. That doesn't mean there are sine waves "in" the pulse. If he had used some other set of basis functions, would that "prove" that those other bases were present in the pulse? Don't get me wrong -- I'm ok with you saying there's RF energy in the pulse, but not with your extrapolation to "RF sine waves." We're talking about impulses here. Why not just say the world is still flat? If lightning did not have so much energy in RF, then radios would not receive that RF noise. The radios are responding to the pulses. Fourier series are a useful way to analyze the response. But the radio is essentially a filter that alters the signal it sees. It's not locking on to some RF sine wave as you seem to think. An example that demonstrates the RF nature of pulses and of lightning. Pulses are not DC. If lightning were DC, then wire impedance would not be relevant. But lets put numbers to it. A 50 foot 20 amp wire may be 0.2 ohms resistance. But wire reactance means same wire has something like 120 ohms impedance to a lightning transient. Sure -- put numbers to it. But show your work. Why is impedance so much larger than the resistance? Because the RF components of lightning make impedance relevant and significant. If lighting were DC, then wire resistance and wire impedance would be same. If lightning were DC, then lightning would not have such destructive consequences. Huh? Have you seen those videos of (as I recall) DC arcs in high voltage transmission tests that are floating around the Web? Fourier analysis demonstrates lightning is AC electricity at many frequencies. Putting a number to the impulse - 8/20 microseconds - explains why so much energy is in the Megahertz range. That's why I asked you for risetime numbers. Show your work. What fraction of the energy is in the MHz range? Using DC analysis to explain lightning means that person never first learned basic transient analysis taught to first year EE students. I haven't noticed anyone here advocating the use of DC analysis per se, so that's a red herring. Lightning has massive energy in radio frequencies which makes lightning so uniquely destructive. Those radio frequencies even mean that an earthing wire bundled with other wires will induce transients on those other wires. DC electricity would not do that inducing. Think pulse. Why are induced transients a problem with lightning? Because lighting is AC electricity - as demonstrated by Fourier analysis, as demonstrated by discussion about impedance, as demonstrated by what first year EE students are taught, as demonstrated by noise on the radio, and as demonstrated by so many industry professional cited in: http://makeashorterlink.com/?X61C23DCA Show me. Show me how lightning is only DC. Who's that addressed to? I never said lightning is only DC. I did say you haven't established it's "AC [or RF] sine waves." Provide supporting facts. Provide industry citations as I have done repeatedly. Declaring something without supporting facts is classic junk science reasoning. Where are those supporting facts, the numbers, and industry professional citations that declare lightning as DC electricity? Without supporting facts, et al, then your claim is really nothing more than personal speculation or urban myth. Show me. Provide facts and numbers. Provide the underlying math. Show me that capacitors and inductors are irrelevant to conducting lightning's DC electricity. Show me rather than make unsubstantiated claims. Show me how you know that lightning is DC electricity. Show me that you also know the difference between ultrasonics and electricity. CJT wrote: That a pulse is susceptible to Fourier analysis does not make it "contain numerous AC sine waves." -- The e-mail address in our reply-to line is reversed in an attempt to minimize spam. Our true address is of the form . |
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#22
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The radio is tuned only to receive a specific frequency.
That pulse is composed of many frequencies. Frequency that interferes with radio reception is a unique sine wave frequency within that pulse. Just one of so many frequencies that create the pulse. Pulses - like all waveforms - are a summation of basic sine waves at different frequencies, amplitudes, and phases. The radio does not receive a pulse. It receives only parts of a waveform that are specific to its tuned frequency. Fourier analysis demonstrates the concept. The radio does not receive a pulse so much as it receives one frequency that was part of that pulse. A chart for the frequency spectrum of lightning is available in: http://www.hubersuhner.com/products/...kb-bas-fre.htm .. What does DC arcing create? That was how radios worked. Sparking DC electricity created AC electricity that resulted in radio waves. Telsa did not transmit DC electricity. To perform electricity transmissions, DC electricity was converted to AC. DC arcing is detected how? By measuring AC components created by that arcing. Meanwhile TimPerry repeatedly refers to DC pulses. That would be DC analysis. Lightning pulse is AC electricity. It creates electromagnetic waves of same frequencies. You even have a chart for that frequency spectrum. What the chart does not show is how the energy content quickly tapers to zero as frequency approaches DC. That pulse called lightning is composed of electricity at RF frequencies. CJT wrote: w_tom wrote: ... Lightning is RF electricity. That RF energy is why lightning even causes noise on radios. So now you say all those RF sine waves, demonstrated by Fourier analysis, really do not exist? You're demonstrating a basic lack of understanding of Fourier analysis. Fourier used the sine function as a basis function. That doesn't mean there are sine waves "in" the pulse. If he had used some other set of basis functions, would that "prove" that those other bases were present in the pulse? Don't get me wrong -- I'm ok with you saying there's RF energy in the pulse, but not with your extrapolation to "RF sine waves." We're talking about impulses here. ... The radios are responding to the pulses. Fourier series are a useful way to analyze the response. But the radio is essentially a filter that alters the signal it sees. It's not locking on to some RF sine wave as you seem to think. ... Huh? Have you seen those videos of (as I recall) DC arcs in high voltage transmission tests that are floating around the Web? |
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#23
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w_tom wrote:
The radio is tuned only to receive a specific frequency. That pulse is composed of many frequencies. The pulse is a pulse. Frequency that interferes with radio reception is a unique sine wave frequency within that pulse. You're really hung up on those sine waves for some reason. Fourier analysis is a mathematical construct (admittedly a very useful one), but it's a fiction (in the best sense of the word). The lightning isn't "created" from sine waves. Just one of so many frequencies that create the pulse. Pulses - like all waveforms - are a summation of basic sine waves at different frequencies, amplitudes, and phases. So what's the phase of the third sine wave in the series? What physical phenomenon results in that phase? Does the Fourier series you contend results in the single lightning pulse match it through all time? Think about what you're saying. The radio does not receive a pulse. Huh? Why not? It receives only parts of a waveform that are specific to its tuned frequency. Fourier analysis demonstrates the concept. The radio does not receive a pulse so much as it receives one frequency that was part of that pulse. So what magic keeps the other parts of the pulse away from the radio? Face it, the radio gets the full pulse and processes it into whatever you hear. A chart for the frequency spectrum of lightning is available in: http://www.hubersuhner.com/products/...kb-bas-fre.htm . Did you look at the scale on that chart? Is that your idea of RF? Looks more like audio to me. What does DC arcing create? That was how radios worked. Sparking DC electricity created AC electricity that resulted in radio waves. Telsa did not transmit DC electricity. To perform electricity transmissions, DC electricity was converted to AC. DC arcing is detected how? By measuring AC components created by that arcing. You're arguing with yourself. I didn't say it was DC (or AC for that matter -- the DC/AC distinction, as explored recently in another thread, is not necessarily useful in a discussion such as this). Meanwhile TimPerry repeatedly refers to DC pulses. That would be DC analysis. Lightning pulse is AC electricity. It creates electromagnetic waves of same frequencies. You even have a chart for that frequency spectrum. What the chart does not show is how the energy content quickly tapers to zero as frequency approaches DC. That pulse called lightning is composed of electricity at RF frequencies. I suspect we're more in agreement than would appear. But my problem with your position is twofold: - your insistence that a pulse in nature is somehow created from lots of sine waves; maybe it's just the words you use, but I have a philosophical problem with projecting a mathematical analysis technique onto nature as more than an analogy - (not explored here yet, but related) your claim in one of your posts that a sharp bend in a ground wire would necessarily destroy its effectiveness in shunting lightning to ground because of effects on its impedance. I think you also contend that wrapping a coil around the wire would cause a similar problem. I assume you would then contend that all skyscrapers run their lightning rod ground wires outside their girder structures, to avoid being encompassed by single turn coils consisting of metallic girders. CJT wrote: w_tom wrote: ... Lightning is RF electricity. That RF energy is why lightning even causes noise on radios. So now you say all those RF sine waves, demonstrated by Fourier analysis, really do not exist? You're demonstrating a basic lack of understanding of Fourier analysis. Fourier used the sine function as a basis function. That doesn't mean there are sine waves "in" the pulse. If he had used some other set of basis functions, would that "prove" that those other bases were present in the pulse? Don't get me wrong -- I'm ok with you saying there's RF energy in the pulse, but not with your extrapolation to "RF sine waves." We're talking about impulses here. ... The radios are responding to the pulses. Fourier series are a useful way to analyze the response. But the radio is essentially a filter that alters the signal it sees. It's not locking on to some RF sine wave as you seem to think. ... Huh? Have you seen those videos of (as I recall) DC arcs in high voltage transmission tests that are floating around the Web? -- The e-mail address in our reply-to line is reversed in an attempt to minimize spam. Our true address is of the form . |
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#24
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w_tom wrote:
The radio is tuned only to receive a specific frequency. That pulse is composed of many frequencies. Frequency that interferes with radio reception is a unique sine wave frequency within that pulse. Just one of so many frequencies that create the pulse. Pulses - like all waveforms - are a summation of basic sine waves at different frequencies, amplitudes, and phases. The radio does not receive a pulse. It receives only parts of a waveform that are specific to its tuned frequency. Fourier analysis demonstrates the concept. The radio does not receive a pulse so much as it receives one frequency that was part of that pulse. A chart for the frequency spectrum of lightning is available in: http://www.hubersuhner.com/products/...kb-bas-fre.htm snip BTW, here's another page in that same series: http://www.hubersuhner.com/mozilla/p...-bas-espec.htm I guess you would have to claim there's positive AC and negative AC to be consistent with it. -- The e-mail address in our reply-to line is reversed in an attempt to minimize spam. Our true address is of the form . |
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#25
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You are hung up on a pulse. True, the sine waves that
combine to create a pulse exist with boundary conditions. A true sine wave goes forever - has no boundary conditions. But how do we measure the frequency response of circuits? We apply a signal that is chock full of 'sine waves' at various frequencies (for a limited time - the boundary condition) and then learn which sine waves come out the other end. We apply a pulse. We measure those 'sine waves' with a spectrum analyzer. If pulses did not create sine waves at all those frequencies, then the spectrum analyzer would do nothing useful. Just another example of how a pulse is far more than just a pulse. A radio receives electromagnetic radiation at its tuned frequency (assuming the signal is not so strong as to overwhelm filters). If a pulse is only a pulse then the radio does not receive anything. But since a pulse is AC electricity at numerous frequencies, then the radio receives only its unique frequency from that pulse. I made it easy. Chart provides a frequency spectrum for a lightning pulse. How can the pulse have a frequency spectrum if a pulse is only a pulse? Yes some of those RF frequencies are so low as to be same as audio frequencies. But they are electrical - not mechanical motion. The electricity is still RF frequencies. Some of the most destructive energy is found in those higher (and less amplitude) frequencies. I guess you are finally coming to accept the fact that a lightning pulse is not just a pulse (and not a DC pulse as TimPerry claimed). You don't provide any supporting facts, numbers, or citations for your claim that "a pulse is only a pulse". Provided were numerous reasons why a lightning pulse is composed of AC electricity at numerous RF frequencies. Numerous sine waves summed together to create a pulse. To repeat some supporting facts: We measure the frequency spectrum of a pulse because a pulse is composed of so many different frequencies. That lightning pulse is affected by impedance because it contains radio frequencies - not DC. The pulse contains frequencies that create noise on tuned radios. Wire impedance created by sharp wire bends can undermine a protection system because lightning is composed of AC electricity. A chart with the frequency spectrum for a lightning pulse is provided showing energy even at the megahertz range. The so called DC arc is really AC electricity. Even Fourier analysis demonstrates that all waveforms (such as pulses) are summations of sine waves at various amplitudes, frequencies, and phases. Lighting pulse contains many sine waves (with boundary conditions). The sharper that pulse, then the more frequencies are contained in a pulse. Meanwhile your concept of earthing a steel building is flawed. The steel frame is sufficient to be an earth ground. It does not have high impedance to obstruct a lightning strike. However, for better protection, the lightning rod is earthed using wire outside the building. Better protection means a building's earthing meets lightning rod's earthing at a point beneath the building - the single point grounding concept. A building structure is not some big 'lightning impeding' inductor. However even wire has impedance which is why shorter connections to earth ground mean superior lightning protection. Wire impedance is also why plug-in protectors are not effectively earthed. Lastly cited is how BT and other telcos earth their switching stations to not suffer lightning damage. Every incoming wire is earthed ideally 50 meters before those wires connect to the computer. Connection from each incoming wire to earth is as short as possible. A larger separation between 'earthing connection to computer' provides more impedance - better computer protection. Short connection 'from incoming wire to earth' means less impedance - a better path for lightning. Why do we mention this? Because lightning protection is about low impedance earthing. Better lightning protection means the protector is where utility wires enter the building, with a shortest connection to a single point earth ground, and not adjacent to electronics. A lightning pulse is not just a pulse. Lightning is many AC waves in a wide frequency spectrum - AC electricity - that seeks earth ground. Protection from lightning involves RF principles that radio engineers best appreciate. CJT wrote: w_tom wrote: The radio is tuned only to receive a specific frequency. That pulse is composed of many frequencies. The pulse is a pulse. Frequency that interferes with radio reception is a unique sine wave frequency within that pulse. You're really hung up on those sine waves for some reason. Fourier analysis is a mathematical construct (admittedly a very useful one), but it's a fiction (in the best sense of the word). The lightning isn't "created" from sine waves. Just one of so many frequencies that create the pulse. Pulses - like all waveforms - are a summation of basic sine waves at different frequencies, amplitudes, and phases. So what's the phase of the third sine wave in the series? What physical phenomenon results in that phase? Does the Fourier series you contend results in the single lightning pulse match it through all time? Think about what you're saying. The radio does not receive a pulse. Huh? Why not? It receives only parts of a waveform that are specific to its tuned frequency. Fourier analysis demonstrates the concept. The radio does not receive a pulse so much as it receives one frequency that was part of that pulse. So what magic keeps the other parts of the pulse away from the radio? Face it, the radio gets the full pulse and processes it into whatever you hear. A chart for the frequency spectrum of lightning is available in: http://www.hubersuhner.com/products/...kb-bas-fre.htm . Did you look at the scale on that chart? Is that your idea of RF? Looks more like audio to me. What does DC arcing create? That was how radios worked. Sparking DC electricity created AC electricity that resulted in radio waves. Telsa did not transmit DC electricity. To perform electricity transmissions, DC electricity was converted to AC. DC arcing is detected how? By measuring AC components created by that arcing. You're arguing with yourself. I didn't say it was DC (or AC for that matter -- the DC/AC distinction, as explored recently in another thread, is not necessarily useful in a discussion such as this). Meanwhile TimPerry repeatedly refers to DC pulses. That would be DC analysis. Lightning pulse is AC electricity. It creates electromagnetic waves of same frequencies. You even have a chart for that frequency spectrum. What the chart does not show is how the energy content quickly tapers to zero as frequency approaches DC. That pulse called lightning is composed of electricity at RF frequencies. I suspect we're more in agreement than would appear. But my problem with your position is twofold: - your insistence that a pulse in nature is somehow created from lots of sine waves; maybe it's just the words you use, but I have a philosophical problem with projecting a mathematical analysis technique onto nature as more than an analogy - (not explored here yet, but related) your claim in one of your posts that a sharp bend in a ground wire would necessarily destroy its effectiveness in shunting lightning to ground because of effects on its impedance. I think you also contend that wrapping a coil around the wire would cause a similar problem. I assume you would then contend that all skyscrapers run their lightning rod ground wires outside their girder structures, to avoid being encompassed by single turn coils consisting of metallic girders. |
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#26
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"w_tom" wrote in message ... Point one. Deny citations from industry professionals by refusing to read them. An ostrich does that; not an informed human. Cited are numerous technical papers and other technical facts on lightning - literally a full days worth of reading. Instead TimPerry pretends those citations did not exist in: http://makeashorterlink.com/?X61C23DCA one has no way of knowing who is an "industry professional" and who is a yoyo. A DC pulse is an oxymoron. As confusing as another ridiculous term: DC triangle wave. Either it is a pulse affected by reactance (inductors and capacitors), or it is only DC that completely ignores reactance. One cannot have it both ways. Either it is DC that ignores reactance, or it is a pulse that makes reactance relevant. Which is it? If lightning is DC, then inductance, capacitance, and impedance is not discussed. Why do industry professionals discuss these repeatedly? Because lightning is not DC. Pulses are transient responses - taught in 1st year engineering - an introduction to AC characteristics. AC analysis makes wire inductance and capacitance significant. DC analysis ignores inductance and capacitance. To understand how lightning works - as cited in http://makeashorterlink.com/?X61C23DCA - one cannot pretend lightning is DC. A lightning impulse is an AC or transient event. Lightning is a composition of many frequencies. Show me a DC wave that has frequency components? You cannot. That is the oxymoron of DC pulse. A 'pulse' has AC components. 'DC' has no AC components. Oxymoron. Equally confusing is to say "DC triangle wave" nothing confusing about it to me. if a waveform lies above reference ground it becomes fluctuating DC regardless of its shape, frequency, pulse repetition rate. id just call it a triangle wave or sawtooth or whatever. the DC part is usully understood. you see the electrons are all moving in one direction through a conductor... that's what Direct Current is. when the little suckers stop and reverse direction on a regular basis then voila! we get Alternating Current. .. DC pulse or DC triangle wave - both are oxymorons. Both contain numerous frequency components. Therefore a 'DC pulse' cannot be analyzed using DC analysis. Lightning requires AC analysis. Lightning is not a DC event. shure is. next thing you know you'll be telling me that a flashlight is AC because when you turn it on it has a fast rise time, a finite duration, and a falling edge when you turn it off.... one big square wave.... plus a few harmonics... and a tiny bit of RF. Point two. TimPerry believes a batting cage set in concrete is not conductive. yep that's what i believe. assuming a typical chain link fence type arangement. granted that any insulator has a breakdown point. i beleive that a barefoot boy leaning aginst a batting cage in a thunderstorm is a bad thing. even a boy in wet sneakers. now should said cage be grounded with standard 8 foot rods at each corner and possibly at intermediate points i might feel differently. its just that i have never seen one treated in such a way. (remember we are talking little league here). even in this case i wouldnt be comfortable. a direct hit by approx 20,000 amps is not something i would care to experiance given the choice. in any event, i personally prefer to be at home or on a nice building during lightning storms. after the storm has passed i then go to various locations as needed and reset breakers, make repairs, or go to backup systems. TimPerry should first read those discussions he refused to learn from in: http://makeashorterlink.com/?X61C23DCA sorry, if i cite a reference it will be to an accredited text, validated research paper, or at least a website from a reasonably reputable organization or agency. A most superior earth ground is an Ufer ground. Why? The earthing is through concrete. Had TimPerry first learned what industry professionals teach, then he would have known the batting cage mounted in concrete makes a best earthing ground - exactly like Ufer grounds. But then TimPerry also promotes an oxymoron called 'DC pulse'. Somehow he knows without first learning the facts. If only he had first read those citations and first learned about Ufer grounding. Then he would not have posted, "i dont think so." One should first learn before knowing something. The energy of lightning is AC electricity. TimPerry wrote: citing a newsgroup discussion is not a valid reference. elaborate (and probably inaccurate) discussion as to the exact nature of lightning will not be of benefit to the original poster. a DC pulse is still a DC pulse no amount of wishful thinking will turn it in to AC (granted that there are some aspects that generate RF and perhaps some other characteristics that may be able to be handled by AC analysis) looking at a few of toms 16,900 archived posts i see he also claims that a ground rod in rock will make a perfectly good ground. from that it follows that a batting cage set in concrete is adiquitly grounded. i dont think so. |
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#27
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w_tom,
While you are correct in many ways, CJT is also correct in pointing out that your suggestion that lightning is made of sine waves is faulty application of Fourier. You could just as easily say that lightning is made of wavelets (and more correctly, actually) or many other functions. These are all just mathematical constructs to describe a complex phenomenon as components that can be manipulated for analysis. The point that lightning is a pulse and can be analyzed by its component frequencies should be clear. That it is "made of sine waves" is an equally clearly faulty application of the concept. If you would learn to be a bit more humble in accepting criticism of your language, useage, and out of context application of concepts, the correct basis of your arguments might be more often appreciated. Mostly, you end up looking like an idiot. Leonard "w_tom" wrote in message ... You are hung up on a pulse. True, the sine waves that combine to create a pulse exist with boundary conditions. A true sine wave goes forever - has no boundary conditions. But how do we measure the frequency response of circuits? We apply a signal that is chock full of 'sine waves' at various frequencies (for a limited time - the boundary condition) and then learn which sine waves come out the other end. We apply a pulse. We measure those 'sine waves' with a spectrum analyzer. If pulses did not create sine waves at all those frequencies, then the spectrum analyzer would do nothing useful. Just another example of how a pulse is far more than just a pulse. |
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#28
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"w_tom" bravely wrote to "All" (07 Jul 05 22:29:12)
--- on the heady topic of " Lightning protection" w_ From: w_tom w_ Xref: aeinews sci.electronics.repair:52721 w_ Meanwhile TimPerry repeatedly refers to DC pulses. That w_ would be DC analysis. Lightning pulse is AC electricity. It w_ creates electromagnetic waves of same frequencies. You even w_ have a chart for that frequency spectrum. What the chart does w_ not show is how the energy content quickly tapers to zero as w_ frequency approaches DC. That pulse called lightning is w_ composed of electricity at RF frequencies. He is not completely wrong, Tom. There is a phenomenon of charge separation which takes place in the cloud and there is a DC potential. The initial discharge starts with DC but with distance and motion we have the effects of inductance and capacitance which establish an impedance and results in reflections where discontinuities exist for a moving wavefront. What we basically have is a square wave going from one DC potential to ground but, like the Fourrier model, made up of an infinite series of sine waves. So yes, there will be AC but the initial natural process is all about charge separation in the clouds. It can be no other way. A*s*i*m*o*v .... Power is obtained by current meeting resistance |
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#29
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w_tom wrote:
You are hung up on a pulse. True, the sine waves that combine to create a pulse exist with boundary conditions. A true sine wave goes forever - has no boundary conditions. But how do we measure the frequency response of circuits? We apply a signal that is chock full of 'sine waves' at various frequencies (for a limited time - the boundary condition) and then learn which sine waves come out the other end. We apply a pulse. We measure those 'sine waves' with a spectrum analyzer. If pulses did not create sine waves at all those frequencies, then the spectrum analyzer would do nothing useful. Just another example of how a pulse is far more than just a pulse. Certainly pulses can excite tuned circuits. That's different from what you have been saying. A radio receives electromagnetic radiation at its tuned frequency (assuming the signal is not so strong as to overwhelm filters). If a pulse is only a pulse then the radio does not receive anything. But since a pulse is AC electricity at numerous frequencies, then the radio receives only its unique frequency from that pulse. I made it easy. Chart provides a frequency spectrum for a lightning pulse. How can the pulse have a frequency spectrum if a pulse is only a pulse? Yes some of those RF frequencies are so low as to be same as audio frequencies. But they are electrical - not mechanical motion. The electricity is still RF frequencies. Some of the most destructive energy is found in those higher (and less amplitude) frequencies. You seem to be using "RF frequencies" to mean "electromagnetic radiation." I think that's another example of imprecise language. I guess you are finally coming to accept the fact that a lightning pulse is not just a pulse (and not a DC pulse as TimPerry claimed). You don't provide any supporting facts, numbers, or citations for your claim that "a pulse is only a pulse". Provided were numerous reasons why a lightning pulse is composed of AC electricity at numerous RF frequencies. I've deliberately steered clear of the DC vs AC controversy. If pressed, I'd probably come down on the side of TimPerry, because I find his flashlight analogy persuasive. But I don't think the distinction is particularly useful, so I find it uninteresting. You and TimPerry could probably resolve your differences by careful definition of the terms DC and AC. I suspect that under your definition, there has never been a true DC (i.e. unvarying, as I understand your position) source. Numerous sine waves summed together to create a pulse. To repeat some supporting facts: We measure the frequency spectrum of a pulse because a pulse is composed of so many different frequencies. That lightning pulse is affected by impedance because it contains radio frequencies - not DC. The pulse contains frequencies that create noise on tuned radios. Wire impedance created by sharp wire bends can undermine a protection system because lightning is composed of AC electricity. Without some calculation to support it, that's a vacuous statement. I think it's probably also incorrect in general. You cited a surge arrestor company's Web site earlier. Do you think the ground wires associated with surge arrestors must similarly avoid sharp bends? A chart with the frequency spectrum for a lightning pulse is provided showing energy even at the megahertz range. The so called DC arc is really AC electricity. Even Fourier analysis demonstrates that all waveforms (such as pulses) are summations of sine waves at various amplitudes, frequencies, and phases. At the risk of sounding too much like a former President, that depends on your definition of "are." "Can be analyzed for certain purposes as if they were" might be closer to the truth. Lighting pulse contains many sine waves (with boundary conditions). The sharper that pulse, then the more frequencies are contained in a pulse. Meanwhile your concept of earthing a steel building is flawed. The steel frame is sufficient to be an earth ground. It does not have high impedance to obstruct a lightning strike. However, for better protection, the lightning rod is earthed using wire outside the building. Better protection means a building's earthing meets lightning rod's earthing at a point beneath the building - the single point grounding concept. A building structure is not some big 'lightning impeding' inductor. However even wire has impedance which is why shorter connections to earth ground mean superior lightning protection. Wire impedance is also why plug-in protectors are not effectively earthed. Apparently I was unclear. :-) I'm not aware of any requirement that the wire grounding a lightning rod not be encircled at any point by the building's girders. Another post of yours seemed to imply such a requirement. Lastly cited is how BT and other telcos earth their switching stations to not suffer lightning damage. Every incoming wire is earthed ideally 50 meters before those wires connect to the computer. Connection from each incoming wire to earth is as short as possible. A larger separation between 'earthing connection to computer' provides more impedance - better computer protection. Short connection 'from incoming wire to earth' means less impedance - a better path for lightning. Why do we mention this? Because lightning protection is about low impedance earthing. Better lightning protection means the protector is where utility wires enter the building, with a shortest connection to a single point earth ground, and not adjacent to electronics. A lightning pulse is not just a pulse. Lightning is many AC waves in a wide frequency spectrum - AC electricity - that seeks earth ground. Protection from lightning involves RF principles that radio engineers best appreciate. CJT wrote: w_tom wrote: The radio is tuned only to receive a specific frequency. That pulse is composed of many frequencies. The pulse is a pulse. Frequency that interferes with radio reception is a unique sine wave frequency within that pulse. You're really hung up on those sine waves for some reason. Fourier analysis is a mathematical construct (admittedly a very useful one), but it's a fiction (in the best sense of the word). The lightning isn't "created" from sine waves. Just one of so many frequencies that create the pulse. Pulses - like all waveforms - are a summation of basic sine waves at different frequencies, amplitudes, and phases. So what's the phase of the third sine wave in the series? What physical phenomenon results in that phase? Does the Fourier series you contend results in the single lightning pulse match it through all time? Think about what you're saying. The radio does not receive a pulse. Huh? Why not? It receives only parts of a waveform that are specific to its tuned frequency. Fourier analysis demonstrates the concept. The radio does not receive a pulse so much as it receives one frequency that was part of that pulse. So what magic keeps the other parts of the pulse away from the radio? Face it, the radio gets the full pulse and processes it into whatever you hear. A chart for the frequency spectrum of lightning is available in: http://www.hubersuhner.com/products/...kb-bas-fre.htm . Did you look at the scale on that chart? Is that your idea of RF? Looks more like audio to me. What does DC arcing create? That was how radios worked. Sparking DC electricity created AC electricity that resulted in radio waves. Telsa did not transmit DC electricity. To perform electricity transmissions, DC electricity was converted to AC. DC arcing is detected how? By measuring AC components created by that arcing. You're arguing with yourself. I didn't say it was DC (or AC for that matter -- the DC/AC distinction, as explored recently in another thread, is not necessarily useful in a discussion such as this). Meanwhile TimPerry repeatedly refers to DC pulses. That would be DC analysis. Lightning pulse is AC electricity. It creates electromagnetic waves of same frequencies. You even have a chart for that frequency spectrum. What the chart does not show is how the energy content quickly tapers to zero as frequency approaches DC. That pulse called lightning is composed of electricity at RF frequencies. I suspect we're more in agreement than would appear. But my problem with your position is twofold: - your insistence that a pulse in nature is somehow created from lots of sine waves; maybe it's just the words you use, but I have a philosophical problem with projecting a mathematical analysis technique onto nature as more than an analogy - (not explored here yet, but related) your claim in one of your posts that a sharp bend in a ground wire would necessarily destroy its effectiveness in shunting lightning to ground because of effects on its impedance. I think you also contend that wrapping a coil around the wire would cause a similar problem. I assume you would then contend that all skyscrapers run their lightning rod ground wires outside their girder structures, to avoid being encompassed by single turn coils consisting of metallic girders. -- The e-mail address in our reply-to line is reversed in an attempt to minimize spam. Our true address is of the form . |
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#30
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The term DC pulses is an oxymoron. However Asimov is
correct. There must be a DC component to a frequency spectrum for current. Problem is that most professional sources say the frequency spectrum for that lightning pulse drops off as frequency decreases. Some put lower frequency limits at 1 Hz. Others at 0.1 Hz. IOW the DC component that does exist would be too small to be considered. Again I don't really understand why this would be true. When the pulse is done, positive and negative charges have been neutralized by a unidirectional flow of electrons. The frequency spectrum from http://www.hubersuhner.com does not show this fall off at lowest frequencies. But the chart also does not show frequencies below 1 Hz. At any rate, perspective of this discussion is Lightning protection. (Although it originally was about a faraday cage provided by a chain link cage), it has morphed into the AC nature of lightning; the component that makes lightning so challenging and destructive. So challenging that some call lightning capricious. The AC component in lightning that make protection difficult is not intuitively obvious. The components that tend to be most challenging are in the kilohertz and megahertz range. IOW the DC component is rarely considered in the overall design of lightning protection. Higher frequency components are discussed as if higher frequencies are the only part that exists. Asimov wrote: He is not completely wrong, Tom. There is a phenomenon of charge separation which takes place in the cloud and there is a DC potential. The initial discharge starts with DC but with distance and motion we have the effects of inductance and capacitance which establish an impedance and results in reflections where discontinuities exist for a moving wavefront. What we basically have is a square wave going from one DC potential to ground but, like the Fourrier model, made up of an infinite series of sine waves. So yes, there will be AC but the initial natural process is all about charge separation in the clouds. It can be no other way. |
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#31
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Yo-yos are easily separated from industry professionals.
Yo-yos post claims without numbers, supporting facts, and experimental evidence (examples). IOW they post junk science. Junk scientists especially fear to provide numbers. Why? Numbers identify myth purveyors from the educated. To promote myths, one must not provide numbers that can be challenged. For example, others may recommend an APC power strip protector. They claim it will block or stop surges? So how does a transient that was not stopped by 3 miles of air get stopped by a one inch part? More damning numbers. The manufacturer's own specifications also make that obvious. Therefore yo-yos avoid saying what the plug-in protector even does. They don't cite joules (a number). They don't cite the manufacturer's specifications. They don't have any idea how its internal components (MOVs) operate. Some are so foolishly deceived into thinking MOVs vaporize (fail catastrophically) to provide protection. They don't even know the so called protected appliance still connects directly to AC mains - nothing between the appliance and wall receptacle wire. They claim a ground light is reporting the existence of an earth ground. They claim the OK light reports the protector as fully functional. So that yo-yos are not exposed, they don't provide any supporting facts and numbers. Notice why my every post is so long? Numerous supporting facts, electrical principles, numbers, and examples are also provided. Its a classic lesson from propaganda experts. Declare the other as wrong AND say no more. The naive among us will then believe the shortest post that only says, "wrong" rather than the longer post that provides supporting reasons why. Some people will always believe a sound byte and deny even principles taught in high school science. Numerous responsible industry professionals were cited in that discussion. Everything from Sun Microsystem's Server Installation manual, National Electrical Code, and even peer reviewed IEEE papers. The benchmark in protection is Polyphaser. Their application notes are legendary. And if that were not enough, visit a newsgroup where lightning is a most serious problem - where direct lightning strikes are routinely earthed without damage: rec.radio.amateur.antenna Those with technical knowledge will appreciate the underlying concepts, solutions, and personal experience provided by posters such as Richard Harrison and Jack Painter. Principles that were even demonstrated by Ben Franklin in 1752. Yo-yos, however, will only make declarations; never provide critical supporting facts, principles, numbers, and real world experience. Ironic that TimPerry would say DC triangle waves are not confusing since that is not what he said on 11 Jun 2005 in the newsgroup sci.electronics.basics entitled "DC Wave Questions": There are a number of waveforms that go in only one direction relative to ground such as sawtooth waves, square waves, and triangle waves. To refer to these as say a "DC triangle wave" would be equally confusing without further qualification. Meanwhile, concrete is not an insulator as TimPerry would have us believe. Concrete is a conductor. Concrete is why Ufer grounds are a most effective method of protecting transistors ... or protecting munitions (the original purpose of Ufer grounds). TimPerry wrote: "w_tom" wrote in message ... http://makeashorterlink.com/?X61C23DCA one has no way of knowing who is an "industry professional" and who is a yoyo. ... Equally confusing is to say "DC triangle wave" nothing confusing about it to me. if a waveform lies above reference ground it becomes fluctuating DC regardless of its shape, frequency, pulse repetition rate. id just call it a triangle wave or sawtooth or whatever. the DC part is usully understood. you see the electrons are all moving in one direction through a conductor... that's what Direct Current is. when the little suckers stop and reverse direction on a regular basis then voila! we get Alternating Current. DC pulse or DC triangle wave - both are oxymorons. Both contain numerous frequency components. Therefore a 'DC pulse' cannot be analyzed using DC analysis. Lightning requires AC analysis. Lightning is not a DC event. shure is. next thing you know you'll be telling me that a flashlight is AC because when you turn it on it has a fast rise time, a finite duration, and a falling edge when you turn it off.... one big square wave.... plus a few harmonics... and a tiny bit of RF. Point two. TimPerry believes a batting cage set in concrete is not conductive. yep that's what i believe. assuming a typical chain link fence type arangement. granted that any insulator has a breakdown point. i beleive that a barefoot boy leaning aginst a batting cage in a thunderstorm is a bad thing. even a boy in wet sneakers. now should said cage be grounded with standard 8 foot rods at each corner and possibly at intermediate points i might feel differently. its just that i have never seen one treated in such a way. (remember we are talking little league here). even in this case i wouldnt be comfortable. a direct hit by approx 20,000 amps is not something i would care to experiance given the choice. in any event, i personally prefer to be at home or on a nice building during lightning storms. after the storm has passed i then go to various locations as needed and reset breakers, make repairs, or go to backup systems. TimPerry should first read those discussions he refused to learn from in: http://makeashorterlink.com/?X61C23DCA sorry, if i cite a reference it will be to an accredited text, validated research paper, or at least a website from a reasonably reputable organization or agency. ... |
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#32
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I appreciate what CJT is saying which is why I included the
concept of boundary conditions. However to be more technically correct, then most readers would not understand the concepts. Yes, sine waves go forever in time. The 'sine waves' that combine to construct a pulse have boundary conditions; exist only during the period of that pulse. Wavelet as a better description would be nice. But I believe most don't even know what a wavelet is. I would not even know how to begin to describe a lightning pulse in terms of wavelets. Where would we even start? Define a pulse in terms of a Daubechie, Mexican Hat, or Morlet wavelet? I think not. Furthermore, I was not sure of CJT's math background. For example, what is a true impulse? Literally every frequency in that spectrum. But did CJT understand that basic math concept? I thought not after a few posts suggested I had better keep it simpler: describe a pulse in terms that all may understand - sine waves. Then made the concept a little more complicated - added boundary conditions. Wavelets - way too complex. To comprehend the destructive (almost capricious) nature of lightning, it is simply better to limit a lightning pulse description to a wide spectrum of frequencies (numerous sine waves of different frequencies that are summed together). Leonard Caillouet wrote: w_tom, While you are correct in many ways, CJT is also correct in pointing out that your suggestion that lightning is made of sine waves is faulty application of Fourier. You could just as easily say that lightning is made of wavelets (and more correctly, actually) or many other functions. These are all just mathematical constructs to describe a complex phenomenon as components that can be manipulated for analysis. The point that lightning is a pulse and can be analyzed by its component frequencies should be clear. That it is "made of sine waves" is an equally clearly faulty application of the concept. If you would learn to be a bit more humble in accepting criticism of your language, useage, and out of context application of concepts, the correct basis of your arguments might be more often appreciated. Mostly, you end up looking like an idiot. Leonard |
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#33
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Pulses are sums of numerous frequencies - numerous sine
waves. A pulse is not just a pulse. Like all waveforms, the pulse is also a sum of various sine waves (of different frequency, amplitude, and phase). IOW a pulse is not just a pulse. A pulse is what happens when numerous sine waves (with boundary conditions) are summed together. That is also true of lightning. Lightning is not some DC pulse. Lightning is AC electricity - at numerous radio frequencies. I was trying to be clear. Lighting is electricity. But the electricity called lightning does create electromagnetic waves that will be of same frequency. Ground wires from any surge protector must avoid sharp bends. As I have so often done, a published source: US Army Training Manual 5-690 3.4 Lightning protection subsystem (p 46) d.1(i) Installation of surge arresters is shown for grounded and ungrounded service ... In order to prevent introducing excessive inductance and resistance in the transient path to the surge arrester, No. 4 AWG (minimum) insulated stranded copper wire of the minimum feasible length must be used to make the interconnection(s) unless otherwise recommended and guaranteed by the manufacturer. Also, the interconnecting wiring must not contain loops or sharp bends. Otherwise, the response time of the surge arrester will be delayed and a higher clamp voltage than that of the surge arrester will be impressed across the protected equipment, thus increasing the possibility of damage. In the event a very fast transient should occur, it is quite likely that the surge arrester would never turn on, and all of the transient energy would be dissipated by supposedly protected equipment. I never said the earthing wire for a lightning rod must not be surrounded by a building's girders. I only said the preferred method of routing that earthing wire is to keep it outside the building. This for reasons beyond the scope of this discussion which is impedance, the purpose of earthing, and characteristics of a lightning pulse that makes it so challenging. CJT wrote: Certainly pulses can excite tuned circuits. That's different from what you have been saying. A radio receives electromagnetic radiation at its tuned frequency (assuming the signal is not so strong as to overwhelm filters). If a pulse is only a pulse then the radio does not receive anything. But since a pulse is AC electricity at numerous frequencies, then the radio receives only its unique frequency from that pulse. I made it easy. Chart provides a frequency spectrum for a lightning pulse. How can the pulse have a frequency spectrum if a pulse is only a pulse? Yes some of those RF frequencies are so low as to be same as audio frequencies. But they are electrical - not mechanical motion. The electricity is still RF frequencies. Some of the most destructive energy is found in those higher (and less amplitude) frequencies. You seem to be using "RF frequencies" to mean "electromagnetic radiation." I think that's another example of imprecise language. I guess you are finally coming to accept the fact that a lightning pulse is not just a pulse (and not a DC pulse as TimPerry claimed). You don't provide any supporting facts, numbers, or citations for your claim that "a pulse is only a pulse". Provided were numerous reasons why a lightning pulse is composed of AC electricity at numerous RF frequencies. I've deliberately steered clear of the DC vs AC controversy. If pressed, I'd probably come down on the side of TimPerry, because I find his flashlight analogy persuasive. But I don't think the distinction is particularly useful, so I find it uninteresting. You and TimPerry could probably resolve your differences by careful definition of the terms DC and AC. I suspect that under your definition, there has never been a true DC (i.e. unvarying, as I understand your position) source. Numerous sine waves summed together to create a pulse. To repeat some supporting facts: We measure the frequency spectrum of a pulse because a pulse is composed of so many different frequencies. That lightning pulse is affected by impedance because it contains radio frequencies - not DC. The pulse contains frequencies that create noise on tuned radios. Wire impedance created by sharp wire bends can undermine a protection system because lightning is composed of AC electricity. Without some calculation to support it, that's a vacuous statement. I think it's probably also incorrect in general. You cited a surge arrestor company's Web site earlier. Do you think the ground wires associated with surge arrestors must similarly avoid sharp bends? A chart with the frequency spectrum for a lightning pulse is provided showing energy even at the megahertz range. The so called DC arc is really AC electricity. Even Fourier analysis demonstrates that all waveforms (such as pulses) are summations of sine waves at various amplitudes, frequencies, and phases. At the risk of sounding too much like a former President, that depends on your definition of "are." "Can be analyzed for certain purposes as if they were" might be closer to the truth. Lighting pulse contains many sine waves (with boundary conditions). The sharper that pulse, then the more frequencies are contained in a pulse. Meanwhile your concept of earthing a steel building is flawed. The steel frame is sufficient to be an earth ground. It does not have high impedance to obstruct a lightning strike. However, for better protection, the lightning rod is earthed using wire outside the building. Better protection means a building's earthing meets lightning rod's earthing at a point beneath the building - the single point grounding concept. A building structure is not some big 'lightning impeding' inductor. However even wire has impedance which is why shorter connections to earth ground mean superior lightning protection. Wire impedance is also why plug-in protectors are not effectively earthed. Apparently I was unclear. :-) I'm not aware of any requirement that the wire grounding a lightning rod not be encircled at any point by the building's girders. Another post of yours seemed to imply such a requirement. Lastly cited is how BT and other telcos earth their switching stations to not suffer lightning damage. Every incoming wire is earthed ideally 50 meters before those wires connect to the computer. Connection from each incoming wire to earth is as short as possible. A larger separation between 'earthing connection to computer' provides more impedance - better computer protection. Short connection 'from incoming wire to earth' means less impedance - a better path for lightning. Why do we mention this? Because lightning protection is about low impedance earthing. Better lightning protection means the protector is where utility wires enter the building, with a shortest connection to a single point earth ground, and not adjacent to electronics. A lightning pulse is not just a pulse. Lightning is many AC waves in a wide frequency spectrum - AC electricity - that seeks earth ground. Protection from lightning involves RF principles that radio engineers best appreciate. CJT wrote: w_tom wrote: The radio is tuned only to receive a specific frequency. That pulse is composed of many frequencies. The pulse is a pulse. Frequency that interferes with radio reception is a unique sine wave frequency within that pulse. You're really hung up on those sine waves for some reason. Fourier analysis is a mathematical construct (admittedly a very useful one), but it's a fiction (in the best sense of the word). The lightning isn't "created" from sine waves. Just one of so many frequencies that create the pulse. Pulses - like all waveforms - are a summation of basic sine waves at different frequencies, amplitudes, and phases. So what's the phase of the third sine wave in the series? What physical phenomenon results in that phase? Does the Fourier series you contend results in the single lightning pulse match it through all time? Think about what you're saying. The radio does not receive a pulse. Huh? Why not? It receives only parts of a waveform that are specific to its tuned frequency. Fourier analysis demonstrates the concept. The radio does not receive a pulse so much as it receives one frequency that was part of that pulse. So what magic keeps the other parts of the pulse away from the radio? Face it, the radio gets the full pulse and processes it into whatever you hear. A chart for the frequency spectrum of lightning is available in: http://www.hubersuhner.com/products/...kb-bas-fre.htm . Did you look at the scale on that chart? Is that your idea of RF? Looks more like audio to me. What does DC arcing create? That was how radios worked. Sparking DC electricity created AC electricity that resulted in radio waves. Telsa did not transmit DC electricity. To perform electricity transmissions, DC electricity was converted to AC. DC arcing is detected how? By measuring AC components created by that arcing. You're arguing with yourself. I didn't say it was DC (or AC for that matter -- the DC/AC distinction, as explored recently in another thread, is not necessarily useful in a discussion such as this). Meanwhile TimPerry repeatedly refers to DC pulses. That would be DC analysis. Lightning pulse is AC electricity. It creates electromagnetic waves of same frequencies. You even have a chart for that frequency spectrum. What the chart does not show is how the energy content quickly tapers to zero as frequency approaches DC. That pulse called lightning is composed of electricity at RF frequencies. I suspect we're more in agreement than would appear. But my problem with your position is twofold: - your insistence that a pulse in nature is somehow created from lots of sine waves; maybe it's just the words you use, but I have a philosophical problem with projecting a mathematical analysis technique onto nature as more than an analogy - (not explored here yet, but related) your claim in one of your posts that a sharp bend in a ground wire would necessarily destroy its effectiveness in shunting lightning to ground because of effects on its impedance. I think you also contend that wrapping a coil around the wire would cause a similar problem. I assume you would then contend that all skyscrapers run their lightning rod ground wires outside their girder structures, to avoid being encompassed by single turn coils consisting of metallic girders. -- The e-mail address in our reply-to line is reversed in an attempt to minimize spam. Our true address is of the form . |
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#34
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w_tom wrote:
snip At any rate, perspective of this discussion is Lightning protection. (Although it originally was about a faraday cage provided by a chain link cage), it has morphed into the AC nature of lightning; the component that makes lightning so challenging and destructive. So challenging that some call lightning capricious. The AC component in lightning that make protection difficult is not intuitively obvious. The components that tend to be most challenging are in the kilohertz and megahertz range. IOW the DC component is rarely considered in the overall design of lightning protection. Higher frequency components are discussed as if higher frequencies are the only part that exists. snip Think about what you just wrote. If you size the ground wire to a lightning rod only on the basis of high frequency components, and don't account for the essentially DC component (which can exceed 10,000 amps, according to the Web site you cited earlier), you won't have much protection. -- The e-mail address in our reply-to line is reversed in an attempt to minimize spam. Our true address is of the form . |
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#35
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"Asimov" wrote in message ... "w_tom" bravely wrote to "All" (07 Jul 05 22:29:12) --- on the heady topic of " Lightning protection" w_ From: w_tom w_ Xref: aeinews sci.electronics.repair:52721 w_ Meanwhile TimPerry repeatedly refers to DC pulses. That w_ would be DC analysis. Lightning pulse is AC electricity. It w_ creates electromagnetic waves of same frequencies. You even w_ have a chart for that frequency spectrum. What the chart does w_ not show is how the energy content quickly tapers to zero as w_ frequency approaches DC. That pulse called lightning is w_ composed of electricity at RF frequencies. He is not completely wrong, Tom. alas: this implys i'm not completely right  .There is a phenomenon of charge separation which takes place in the cloud and there is a DC potential. The initial discharge starts with DC but with distance and motion we have the effects of inductance and capacitance which establish an impedance and results in reflections where discontinuities exist for a moving wavefront. What we basically have is a square wave going from one DC potential to ground but, like the Fourrier model, made up of an infinite series of sine waves. So yes, there will be AC but only as a theoretical concept. the electrons only travel on one direction. cloud to earth or earth to cloud, or cloud to cloud. (mostly) but the initial natural process is all about charge separation in the clouds. It can be no other way. A*s*i*m*o*v ... Power is obtained by current meeting resistance This week a master electrician asked me how well versed I was in lightning. I looked him straight in the eye and said "there is no human on the planet that's well versed in lightning". He cracked up and nearly fell down laughing. He then gasped out "that's exactly what I wanted to hear" We then went on to discuss his problem. he had installed some motors with solid state starter circuits in a grain elevator 2 years ago. this year a series of storms has blown the starter/controller on multiple occasions. The frustrated granary owner accused master electrician Frank of installing faulty grounds. I explained that from my viewpoint that the initial causation of equipment damage can be mighty hard determine. Did the lightning come sown the structure? Was it a hit on the power line or transformer? was is a spike caused by brief power interruption? in many cases I am faced with blown fuses, open breakers, transformers that are shorted and sometimes on fire, and sometimes arc holes in equipment cabinets. At this time I am replacing some arc gaps and lighting transformers that were melted by a stroke. The project will cost about $15,000 USD as some aircraft beacons will need to be replaced along with AC cable. We then proceeded to plan the install of a 100 kW generator. I pointed out the parallel solid state TVSS unit and the 4" ferrite toroids on the load side of the 3 phase service. He said "wow does that prevent lightning damage?" I replied when is comes to direct hits by lightning anything can happen but over the long term this and similar arrangements reduce maintenance / repair costs and downtime. for those interested in reading a "white paper" on lightning protection this page http://www.nautel.com/support/files/...protection.pdf may be informative. It is geared toward a specific type of situation. it lists sources. section 2.2 describes lightning characteristics. you may agree or disagree with the data it presents but you may note section 2.2.2 describes a median main lightning strike pulse as a uni-directional near-exponential pulse of 20,000 amperes peak amplitude lasting 40 microseconds to half amplitude. I don't know about you but uni-directional pulse sounds like DC to me. |
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#36
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10,000 amp for what time? Some assume a 12 AWG wire (2mm)
used for 20 amp service will vaporize under higher currents. First that same wire will carry 200 amps continuous without vaporizing. Second, did you notice the word 'continuos'. Now lets limit that current to 40 microseconds. That wire can easily carry 10,000 amps for a short time span. Easily? Well, complications are created when the wire has sharp bends, loops, routed inside metallic conduit, etc. I can appreciate your apprehension. To you, much of this is new. But the technology is old, standard, and well proven for decades. Earthing wires required for AC electric must be so large that the DC component in lightning is irrelevant. Complications are created when that wire is not properly installed so that wire impedance is increased. What makes lightning protection even more challenging is that humans don't learn of their mistakes until after the first lightning strike. Humans made a mistake that only humans can correct. CJT wrote: Think about what you just wrote. If you size the ground wire to a lightning rod only on the basis of high frequency components, and don't account for the essentially DC component (which can exceed 10,000 amps, according to the Web site you cited earlier), you won't have much protection. |
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#37
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Ironic that TimPerry would say DC triangle waves are not
confusing since that is not what he said on 11 Jun 2005 in the newsgroup sci.electronics.basics entitled "DC Wave Questions": There are a number of waveforms that go in only one direction relative to ground such as sawtooth waves, square waves, and triangle waves. To refer to these as say a "DC triangle wave" would be equally confusing without further qualification. an equally long and ultimately fruitless discussion initiated by a student who used the term DC sinewave. please note the wording. neither statemet advocates the use of the phrase "DC wave" "or DC triangle wave" "nothing confusing about it to me. if a waveform lies above reference ground it becomes fluctuating DC regardless of its shape, frequency, pulse repetition rate. id just call it a triangle wave or sawtooth or whatever. the DC part is usully understood." Tom, my objection was to your repeated declaration that "the term DC pulse is an oxymoron". however my statement comes off in a way I did not intend. Please accept my apology. I agree with you that the term DC triangle wave is confusing. Meanwhile, concrete is not an insulator as TimPerry would have us believe. Concrete is a conductor. yee haw we wont need to bother with expensive copper anymore. Just pour us some concrete power lines. Concrete is why Ufer grounds are a most effective method of protecting transistors ... i should wrap all my transistors in concrete? or protecting munitions (the original purpose of Ufer grounds). and the steel rebar has nothing to do with it? |
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#38
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w_tom wrote:
10,000 amp for what time? Some assume a 12 AWG wire (2mm) used for 20 amp service will vaporize under higher currents. First that same wire will carry 200 amps continuous without vaporizing. Second, did you notice the word 'continuos'. Now lets limit that current to 40 microseconds. That wire can easily carry 10,000 amps for a short time span. Easily? Well, complications are created when the wire has sharp bends, loops, routed inside metallic conduit, etc. I can appreciate your apprehension. To you, much of this is new. But the technology is old, standard, and well proven for decades. Earthing wires required for AC electric must be so large that the DC component in lightning is irrelevant. Complications are created when that wire is not properly installed so that wire impedance is increased. What makes lightning protection even more challenging is that humans don't learn of their mistakes until after the first lightning strike. Humans made a mistake that only humans can correct. Your patronizing attitude is starting to get annoying. Your argument can be extended to the "AC" component on which you focus -- if it's all over in 40 microseconds, what's the big deal? :-) CJT wrote: Think about what you just wrote. If you size the ground wire to a lightning rod only on the basis of high frequency components, and don't account for the essentially DC component (which can exceed 10,000 amps, according to the Web site you cited earlier), you won't have much protection. -- The e-mail address in our reply-to line is reversed in an attempt to minimize spam. Our true address is of the form . |
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#39
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w_tom wrote:
That is also true of lightning. Lightning is not some DC pulse. Lightning is AC electricity - at numerous radio frequencies. Isn't the definition of AC electricity whose current changes direction? Are you saying all lightning strikes change direction? Ground wires from any surge protector must avoid sharp bends. As I have so often done, a published source: US Army Training Manual 5-690 3.4 Lightning protection subsystem (p 46) d.1(i) Installation of surge arresters is shown for grounded and ungrounded service ... In order to prevent introducing excessive inductance and resistance in the transient path to the surge arrester, No. 4 AWG (minimum) insulated stranded copper wire of the minimum feasible length must be used to make the interconnection(s) unless otherwise recommended and guaranteed by the manufacturer. Also, the interconnecting wiring must not contain loops or sharp bends. Otherwise, the response time of the surge arrester will be delayed and a higher clamp voltage than that of the surge arrester will be impressed across the protected equipment, thus increasing the possibility of damage. In the event a very fast transient should occur, it is quite likely that the surge arrester would never turn on, and all of the transient energy would be dissipated by supposedly protected equipment. I wonder why they specify insulated wire. Uninsulated wire is easier to inspect and easier to identify as a ground. Stranded wire has less inductance than solid, but what about flat braid? I think it's specified for commercial transmission towers because it has less inductance than stranded wire. If an Army technician had thirty feet of ground wire to connect terminals ten feet apart, he might leave the extra twenty feet taped in a coil halfway between. I agree that a loop like that would be bad. By comparison, how bad would it be to have a sharp bend around a wooden corner? I never said the earthing wire for a lightning rod must not be surrounded by a building's girders. I only said the preferred method of routing that earthing wire is to keep it outside the building. This for reasons beyond the scope of this discussion which is impedance, the purpose of earthing, and characteristics of a lightning pulse that makes it so challenging. An external ground wire would be easy to inspect and less likely to be damaged by humans. Are there more technical reasons? |
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#40
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w_tom wrote:
The term DC pulses is an oxymoron. Isn't DC electrical current that flows in only one direction? In 1883, when a telegraph operator hooked up a battery and started pressing his key, wasn't he generating DC pulses? (There may have been a little AC activity each time the key broke contact.) At any rate, perspective of this discussion is Lightning protection. (Although it originally was about a faraday cage provided by a chain link cage), it has morphed into the AC nature of lightning; the component that makes lightning so challenging and destructive. So challenging that some call lightning capricious. The AC component in lightning that make protection difficult is not intuitively obvious. The components that tend to be most challenging are in the kilohertz and megahertz range. IOW the DC component is rarely considered in the overall design of lightning protection. Higher frequency components are discussed as if higher frequencies are the only part that exists. I don't know if they were familiar with AC when they defined the Henry. Across one Henry of inductance, it takes one Volt to increase the electrical flow by one Ampere per second. Suppose a grounded terminal gets hit by a 1000-Volt pulse lasting .001 second. Suppose the grounding rod has 20 ohms to ground, and there's a 1 Henry choke between the terminal and the rod. The thousand Volts will increase the current through the inductor at 1000 Amperes per second. At the end of 1 millisecond, current will have increased to one Amp. In view of the resistance at the ground rod, voltage will have increased to 20 Volts. Things will be entirely different on the hot side of the choke. What appears to be a short for unvarying DC will appear to be an open for a quick, low-impedance pulse. Who needs AC theory for that? |
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