Lightning protection

[w5rkl]

I've been reading about lighting protection/prevention from links on this forum as well as others. I live in Oklahoma
out in the country where a 160KV power line travels along the edge of my property about 400 feet from
the house. There are two 150 foot tall steel poles supporting the power lines. One pole is within 400 feet of the
house while the second pole is about 700 feet from the house. Each pole is connected at the top by dual heavy gauge
wire. The second pole has 3 switch arms mounted on the top that feed the power substation below and next to
the second pole.

During a recent local line noise hunt with the electric company the tech and I discussed lightning prevention.
The tech, a ham, said I was fairly protected by these tall steel poles. I'm not so sure since my neighbor who
lives about 300 feet farther away from the poles, had his 60 foot tall pine tree directly hit by lightning a
couple of years ago. The "bang" was very loud! I didn't have any damage from an EMP or anything but he
sure did. Lost telephones, Internet router/switch, etc but no fire. Just a very loud instant "BOOM"! I thought
our house was hit but luckily it wasn't. I have two pine trees of the same height as my neighbor which
has one end of my G5RV hung from. They trees are about 100 feet from the rear of the house.

Based on what the electric company tech stated, do these steel poles provide an area of protection
against lightning strikes?

I would never rely on these poles to prevent lightning from striking my antennas which are much lower. That
would be a foolish thing to do! I was just wondering if it is true that a 150 foot tall metal power pole would
provide an area of protection, if any, against lightning strikes?


73
Mike
W5RKL

[WA1GFZ]

no

[The Slab Bacon]

NO, NO, and NO!! I took a lightning hit a couple years back. Of all of the taller stuff it could have hit, it hit the pole light on my garage which was only around 8 -10' off of the ground. (my neighbor watched it happen) Not to mention the high steel HV towers 2 blocks behind me. Lightning is fickle stuff with a mind of its own!! Its gonna do what IT wants to do!!

                                                    The Slab Bacon

[WBear2GCR]

I think the idea is "bleed charge" locally.

If you can't build up a charge differential, there can't be a discharge (lightning).
Thus the stainless steel "chimney brush" on the top of a tower... massive charge bleeding.

At least that is the theory as far as I know...

                      _-_-bear

[w4bfs]

as I recall, GE station engineering had a series of tips on how to limit lightning damage ... bringing coax feedlines through grounded conduits with coiled loops of transmission line outside to act as retarders .. I will try to see if I can find my notes...73...John

[Steve - WB3HUZ]

Yes, it will. Not absolute protection, but more than if it wasn't there (all other things being equal).

[WA1GFZ]

Steve has a point it will help to bleed off a static charge but don't count on it.
Last week someone in our group asked our world known lightning expert if he had rods on his house. He said no but his neighbor did and he liked it that way.
If you are going to have a path make sure it is a good one or you will have a lot of voltage.
Coiled up coax acts like an RF choke to hopefully get the lightning to jump off the shield and go somewhere else.
Rumor has it we are going to lightning school later this year.

[WU2D]

Ah lightning. The best way to attract lightning is to send all the hams in the world out onto the top of a hill during the most active time of year for lightning.
It is called Field Day...

My first field day lightning experience was when I was a wee lad in upstate NY in 1973. Of course us kids were used on 40M and 80M CW exclusively while the OF's talked on SSB. A farmer ham had a great hill with a single big tree and a telephone pole on top. We had one of the WW2 surplus Jeep generators for great power. The old hams used the trees to hoist dipoles and inveted Vees. Anyway this young hippie professor from Clarkson shows up with this fancy new radio called a FT-101. Nobody had seen this kind of radio before. Anyway this guy claimed to be a CW bug-man and wanted to do 20M. The old F's already had a tribander on a guyed ladder on 20M so they told him to go to 15M.

Anyway, he had a big spool of wire and he told us kids to run the wire down the hill in the various trees in a fairly straight line. I think we walked out at least 500 feet of wire. Then he showed us his secret weapon - the random wire un-tuner.

We had a little RF in the pop-up upon tune up so a primitive ground rod was lashed up and things settled down.

Later that day the clouds formed and when we were sure that a big storm was heading our way, my elmer wisely told me to head for the car. Before going down however, I checked in with the prof. There was a low tone coming out of his radio which increased in frequency and then a loud pop and flash would occur and the charge up would start all over again. I have no idea how he was not killed. But this is just the typical field day experience.

Mike WU2D

PS Steve,

I had a dog named tax. When I opened the door in come tax.

[Don, W2DL]

As the consulting engineer for three radio stations I attended a lightning seminar some years ago sponsored by the power company and a local college. Bottom line was, a tall object that is a "relatively good" conductor creates a "cone of protection" (cone of silence?) around it and it was stated it would be very unlikely to have a hit occur in that area. The "cone of protection" was figured by taking the top of the object - in your case, the 150' high power pole - and then drawing a 30 degree off the vertical cone from that point to the ground. Doing the math for 150 ' tower gives a ground protected area of only 86 ft, not much good for your situation! This "cone of protection" does explain, however, why lightning seldom strikes in Manhatten Island, for example, because almost any place - at least in mid/lower Manhatten - is protected by all the tall buildings and their "cones of protection".

73
Don, W2DL

[w4bfs]

the cone of silence is provided by the lightning strike by following permanent deafness

[Todd, KA1KAQ]

Bottom line was, a tall object that is a "relatively good" conductor creates a "cone of protection" (cone of silence?) around it and it was stated it would be very unlikely to have a hit occur in that area. The "cone of protection" was figured by taking the top of the object - in your case, the 150' high power pole - and then drawing a 30 degree off the vertical cone from that point to the ground. Doing the math for 150 ' tower gives a ground protected area of only 86 ft, not much good for your situation!

This is how I remember it as well: inside the cone, pretty safe (nothing is absolute with lightning). Outside the cone, not so much.

As Steve said, the tall poles nearby do offer limited protection, as 'something' is better than nothing when it comes to a point for a stepped leader to start its journey. But as the neighbor's pine clearly illustrates with respect to lightning - it is what it is.

Ol' Ma Bigelow still tells the story of the night that ball lightning rolled around under my baby crib when we lived in Middletown CT. I was a year old +/-, so no memory. But it might explain a few things.... 

[Bacon, WA3WDR]

For years now, I have been meaning to try something with those chimney-brush dandelion thingies.  I won't do an experiment like this in a neighborhood, because of the danger.  I think maybe some back-woods location would be better.

W2WLR George said that somebody had seen about 2 amperes of corona discharge current in their downlead from those chimney brushes as a storm cloud went overhead.  Because of the enormous voltages present in the clouds, I figure that the corona current will not be very much affected by any reasonable voltage that the ground lead goes to.  If that is correct, then a great deal of power could be collected from such clouds passing overhead - say, 1.8 amps at 10,000 VDC, or maybe 200,000 VDC, etc.

The trick would be to convert from DC to AC efficiently and reliably.

LIGHTNING STRIKES AGAIN
George Bonadio, W2WLR
AM Press/Exchange, Issue 114, February, 1995

[WA1GFZ]

I've been told by real experts the cone of protection is a bunch of BS. I brought it up once and got a real laugh. This is from SAE lightning and RTCA lightning people.....you know the guys who keep the planes in the air.

Big Al K1JCL knows his lightning very well.

I've seen some real commerical radio hack jobs by so called experts.

[w5rkl]

Cone of protection or not, I don't believe it. Yesterday, we had one heck of a thunderstorm with lots of lightning.
About 15 to 30 minutes into the storm lighting hit something very close to the house. The flash, very loud explosion,
and a strange sound like a high pitched growl/groaning was heard in the house. The lights didn't flicker or dim, just the
strange noise along with the lightning flash and loud boom.

My wife said she saw a bright flash coming from the end of the house where the strange high pitched growl/groaning
came from immediately after the lightning flash occurred. After the storm was over, I checked everything, telephones,
televisions, DVD players, ham gear, etc, nothing was damaged. This morning I went outside and checked the trees,
yard, fence, antenna feed line, antennas, and the house. Not a bit of evidence of damage anywhere.

We have UPS's on our computer network, Xyl works from home. Since I couldn't find any damage, I thought maybe the
UPS's made the sound but then again, why didn't the lights change, flicker or dim? The UPS's sounds a beep when power
fails and they have beeped before during a thunderstorm yet the lights never flickered or dimmed. Neither of the UPS's
showed any signs of damage either. I also thought the surge protector power strips may have caused the noise. Again,
they show no signs of damage and not one breaker tripped in the main panel. Very strange!

73
Mike
W5RKL

[K3ZS]

When I was young I had a 14AVQ vertical on the roof of my parent's house.    It was about 30 ft tall with a roof mounted ground plane of two wires on each band.    We lived on top of a hill.    Whenever some clouds that looked like they could produce a thunderstorm came overhead, you could hear arcing in the PL-259 antenna connector.    Sometimes it would hiss.    This connector was disconnected and not grounded.    The voltage build up must have been between the vertical part of the antenna and the elevated groundplane.     There was not always storms nearby when this happened.    However, when there were storms, the arcing would quit as soon as you saw a lightning strike.   I once touched it a got a good shock.    Lightning never hit us though, maybe we were being protected by the antenna discharge.

[Todd, KA1KAQ]

Well, again - with lightning there are no guarantees. But I suspect if such stats were kept, you'd see clearly that places/items located under a cone of protection were struck far less often than outside. Unfortunately, no one keeps track of non-strikes.

Big Al is da man. I have his old 6m Utica w/VFO preserved in the VHF room. Wish he still brought his military shelter complete w/ART-13 station to the 'fests. Gas prices make that a very unattractive endeavor these days.

[WA1GFZ]

I'll put my money on the expert sitting 10 feet away and he has records back to dirt.

[K1JJ]

Interesting thread. Yes, Big Al is the guy who taught me about lightning and ground installations too.

I don't think a pole stuck in the ground is enough to bleed off a big area, like an acre. A radial field under the pole (or tower) is needed cuz the soil itself is such a poor conductor.

I'm a believer in bleeding off the charge to greatly reduce lightning strikes.  This may be "ham anecdotal" info, but back in the 80's we use to get hammered by lightning here. I had a single 150' tower, but no radials... barely grounded with a few 8' rods.  I lost several computers, many telephones, modems and other electrical appliances as a result of strikes.  I learned to disconnect EVERYTHING, including power breakers during storms. Still, I would  lose stuff just from the EM pulse. I live on an 800' hill that sticks out like a sore thumb from a distance.

Fast forward to the 90's. I put up four more towers. Two are 190'ers.  I also installed an elaborate ground system that has 15 miles of radials over a 4 acre area, tied into the towers with an underground trench connecting all towers with #6 wire..  The radials were for a 3 el 160M vertical system, but the lightning benefits were soon realized.   I still disconnect everything when T-storms appear, but I cannot remember when the towers or within 1/8  mile have been hit by lightning. I always listen closely to count the time between the flash and boom and there is at least a one or two second delay.   As a result, I've not lost a single piece of gear to lightning in over 15 years.

The trees around the area (1/8 mile) get hammered as shown by the burned tree trunks I see.

I'm cornvinced that bleeding off the charge is the key to reducing the chances of a strike and requires radials fanned out over the ground. 

I also believe that lightning strikes are triggered by random cosmic rays which begin the path. However, I feel that the lightning path is harder to start if the local ground is bled off compared to surrounding areas.  Also, the top of a hill is not necessarily an attracter - the side gets hit as much or more often.


Bottom line is I feel well grounded towers and other well-distributed charge bleeding systems are a good thing for reducing the hit frequency. 


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