Variations On Lightning Protection For High Voltage Transmission Lines

Thread Starter

Glenn Holland

Joined Dec 26, 2014
705
All high voltage transmission lines are provided with overhead shield wires for lightning protection.

However, the number of shield wires on these lines seems to vary. Some have just one wire attached to the top of the towers, but others have two wires attached to a cross arm. Both of the photos show a two-circuit transmission line (three wires on each side of the tower) and the first one has only one shield wire at the top, but the second has two wires attached to the upper cross arm.

It seems that lightning protection for power lines should be designed in accordance with uniform engineering standards, yet the variations indicate there is some difference in opinion about what is adequate.
 

Attachments

Last edited:

tranzz4md

Joined Apr 10, 2015
310
I'm not a lineman, but I believe that the top cable is actually known as a "static line", and it's configuration is determined by the tower or pole (support structure). It is intended to fall across the line conductors if it fails, to trigger an instant shutdown.
 

GopherT

Joined Nov 23, 2012
8,012
Is it a difference in opinion or a difference in technology evolution? Nobody is going to go back and retrofit hundreds of miles of towers.

Alternatively, design criteria are likely optimized for construction costs vs repair consiquences. That means, labor, steel, transportation and loss of power at factories vs communication vs residential and lost revenue for the utility (or any contractual penalties for lack of service to industrial customers).
 

#12

Joined Nov 30, 2010
18,210
It seems that lightning protection for power lines should be designed in accordance with uniform engineering standards
I'm sure you can find the guilty utility companies and make them bring their equipment up to the proper standards.
Thanks for keeping the power grid safe.;)
 

Thread Starter

Glenn Holland

Joined Dec 26, 2014
705
I found two photos of two circuit transmission lines in the Los Angeles area that were built at about the same time (the 1940s) and they use different configurations for lightning protection.

The first photo shows a double shield wire strung from a "bull's head" cross arm and the second is a single wire strung from the apex of the tower. Since these lines were built in the same city (and in the same era), it seems there should have been a consensus on what constitutes adequate lightning protection. o_O

DPW Transmission Line 1.jpg DPW Transmission Line 2.jpg
 

GopherT

Joined Nov 23, 2012
8,012
I found two photos of two circuit transmission lines in the Los Angeles area that were built at about the same time (the 1940s) and they use different configurations for lightning protection.

The first photo shows a double shield wire strung from a "bull's head" cross arm and the second is a single wire strung from the apex of the tower. Since these lines were built in the same city (and in the same era), it seems there should have been a consensus on what constitutes adequate lightning protection. o_O

View attachment 123918 View attachment 123919
Why do you believe that? Two companies make an analysis of the same variables on a daily basis. Your local grocery stores, automotive companies, clothing manufacturers. They all have business strategies on top of the engineering optimization. One company may have decided the extra expense of two wires is not worth the 99.9% reliability factor and would rather put more repair people in the field. another company decided 99% reliability was too low so they would rather have fewer service calls. A third company likely said they want extra wire in top, and extra service people in the field.

PS: This third company ran to the utility regulators and said we have to raise our prices, we are losing money - but don't let out competitors raise rates because their expenses are so low, they are making excessive profits off your citizens.
 

Thread Starter

Glenn Holland

Joined Dec 26, 2014
705
Why do you believe that? Two companies make an analysis of the same variables on a daily basis. Your local grocery stores, automotive companies, clothing manufacturers. They all have business strategies on top of the engineering optimization. One company may have decided the extra expense of two wires is not worth the 99.9% reliability factor and would rather put more repair people in the field. another company decided 99% reliability was too low so they would rather have fewer service calls. A third company likely said they want extra wire in top, and extra service people in the field.

PS: This third company ran to the utility regulators and said we have to raise our prices, we are losing money - but don't let out competitors raise rates because their expenses are so low, they are making excessive profits off your citizens.
If I were reborn as a phase conduction wire and I had to relive my entire life on a high voltage transmission line, I would definitely want 99% reliability and a lightning protection wire right above me like the ones shown in the first photo!!! :D
 

Thread Starter

Glenn Holland

Joined Dec 26, 2014
705
In the 1940s or thereabouts, experiments for lightning protection were done on scale models in a high voltage lab at General Electric.

The first and second photos are a scale model of a transmission line and the third is a scale model of a small city.

I believe the source of these miniature lightning discharges was a large Van DeGraff generator.

High Volatage Line 1.jpg High Volatage Line 2.jpg High Volatage Line 3.jpg
 

tranzz4md

Joined Apr 10, 2015
310
Actually, it is evident that you are unfamiliar with lightning protection, HV and UHV transmission systems. AAC isn't really a forum for much in the way of high power generation, transmission and distribution. (Have you heard of the IEEE?)

Static lines, balance lines, support structures, conductors, wind loads, lightning protection, voltages, terrain and nearby structures and systems are all different items, and are elements which affect each other on transmission lines and systems.

How familiar are you with the NESC and "the color books"? Facetious and snide remarks aside (as I, too, frequently can't resist making) engineering of these systems and components is in fact substantial, thoroughly regulated, and revolves around safety, efficiency, and durability. Costs are measured far beyond simple material and construction costs.
 
Top