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Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
Any know what companies do to protect their cell-towers from lightning strikes so the equipment does not get destroyed? Lightning is so powerful I find it hard to imagine that a rod can absorb all of the energy without it striking some of the tower wires going to the electronics.
I ask because I am building a wind generator that will be on a 35' tower. Other than grounding the tower and having a lightning rod above the blades I was wondering what else I could do? My current thoughts are: have other structures like higher trees near the pole have arrestors just disconnect the system during a storm
Registered Member #16
Joined: Thu Feb 02 2006, 02:22PM
Location: New Wilmington, PA
Posts: 554
Here in Georgia (second only to FL for lightning) most companies extend the tower about 30' above the cell antennas themselves, and use an umbrella shaped hat on top of the towers that provides a good bit of shielding. This is common on microwave and cell towers, but less so things for lower wavelengths like TV and broadcast radio.
Your three ideas are how hams have dealt with the lightning threat to their antennas since the '20s.
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
Dave, maybe you can give me your thoughts on this idea. I have a Tesla coil that puts out 5' sparks. My formula 65*in^0.7 = kv may be wrong, but using it I get 1Mv. Can I use this to simulate lightning strikes to see how well I'm shielding or diverting the strikes, or is this a waste of time?
My blades are aluminum and they attach to a shaft that runs through the center of the stator. The shaft has an electrical connection with the body which connects to the grounded tower pole. Clearly, I don't want lightning hitting the stator coils, but maybe, if the lightning hits the blades the current will be diverted to the ground. I am just not sure what would happen if a high current pulse goes through the center of the stator. Just so the orientation is pictured correctly, if the shaft is analagous to a tree trunk, the coil cores come off like the branches, and the coils are wrapped around these branches. I am guessing that if the pulse goes through the shaft, the field will expand circumferencially and cut through the coils inducing a current.
Registered Member #1159
Joined: Fri Dec 07 2007, 02:10AM
Location: Hudson Valley of NY State
Posts: 84
Be sure to bond your tower ground to the mains ground. Remember, the earth acts like a big resistor & the voltage drop between those ground rods could be quite large. Very bad ju-ju for anything plugged into the mains.
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
How does bonding directly to the MAINS ground help vs just attaching the tower to a 10' copper pole in the ground? Are you implying that with the Earth resistance the tower voltage will still be 1000's of volts above the Mains ground voltage?
Unless others agree, I find it scary to connect a potential source of lightning to the MAINS ground.
Registered Member #1159
Joined: Fri Dec 07 2007, 02:10AM
Location: Hudson Valley of NY State
Posts: 84
The difference in potential between the tower ground & mains ground could be 10's of thousands of volts, or more depending on how far apart the grounds are & how close the lightning strike is. Bonding all grounds is a common practice in the ham radio community.
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
Thanks, Sparky. Along the lines of lightning protection, is it easy to build a MOV arrestor or should I just buy one? Here is one that I found on-line:
I figure if I find a few that can take high current I can just run some in parallel. Anyone have suggestion on some robust MOVs?
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Lightning protection
