Lightning protection

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:

.

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. Lightn> w_tom wrote:

The pulse is a pulse.

Frequency that

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

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.

Huh? Why not?

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.

Did you look at the scale on that chart? Is that your idea of RF? Looks more like audio to me.

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).

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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BTW, here's another page in that same series:

I guess you would have to claim there's positive AC and negative AC to be consistent with it.

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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 lightn> w_tom wrote:

one has no way of knowing who is an "industry professional" and who is a yoyo.

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

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.

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

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.

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" bravely wrote to "All" (07 Jul 05 22:29:12) --- on the heady topic of "Re: 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

Certainly pulses can excite tuned circuits. That's different from what you have been saying.

You seem to be using "RF frequencies" to mean "electromagnetic radiation." I think that's another example of imprecise language.

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.

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

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

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.

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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

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 discussi> He is not completely wrong, Tom. There is a phenomenon of charge

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":

Meanwhile, c>>

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 lightn> w_tom,

that lightning is made of wavelets

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)

I never said the earth> Certainly pulses can excite tuned circuits. That's different

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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alas: this implys i'm not completely right :).

There is a phenomenon of charge

What we basically have is a square wave going from

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

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

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.

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 lightn> Think about what you just wrote. If you size the ground wire to

since that is not what he said on 11 Jun 2005 in the

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.

yee haw we wont need to bother with expensive copper anymore. Just pour us some concrete power lines.

Concrete is why

i should wrap all my transistors in concrete?

or protecting munitions (the original purpose

and the steel rebar has nothing to do with it?

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?

:-)

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Isn't the definition of AC electricity whose current changes direction? Are you saying all lightning strikes change direction?

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?

An external ground wire would be easy to inspect and less likely to be damaged by humans. Are there more technical reasons?

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.)

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?