Electrical towers have thick, heavy cables for carrying the electrical power to the end user. But, most if not all of these towers have thin wires running along the top of these “animalmorphic” metal structures…why? What is their function? (I know…rest areas for birds!)
No cite so I’m not positive but I believe they act as lightning rods to protect the electrical grid.
They are known as ‘statics’. As billy said, they are there to protect the conductors (the heavy cables you mentioned) as well as any equipment connected to the lines from lightning strikes.
I wish someone would have protected me from “Statics”…and every other mechanical engineering course, too! 
- Jinx
BTW, “high tension” is generally not used in the electrical engineering field. I belive “tension” is French for “voltage,” so that “haute tension” is French for “high voltage.”
(Slightly off topic)
On the main conductors of a transmission line I occasionally see assorted items such as a large ball bolted over each line or what looks like lead weights connected to the line near the tower connections. What do these various accessories do? It doesn’t seem likely that they need a squirrel guard on a 400kV cable.
And here’s another hijack…
Why is it that everytime a parachuter gets tangeled in the wires you see huge sparks fly, and they dead or almost getting killed. They’re not grounded, and even if they were, they wires, I assume, are insulated. Is it just because of the potential difference between the electric field surrounding the wire and the person are enough to cause this to happen??
Joey
I believe these tension lines are often NOT insulated. I think the insulation may break down after years anyway. This may be the reason they are spaced so far apart (one inch per 1000 volts, minimum.) A parachuter will only die if the person is grounded or gets caught between two HOT lines. Maybe, just maybe, if the harness is conductive in some way, the parachuter would feel the benefit of an electrom flow even though his body may not be touching one of the lines.
FYI- insulation is designed to protect against “electric field surrounding the wire”- that is its purpose. Electrons stay in, magnetism comes out. It would be correct to say “magnetic field surrounding the wire”, if insulated.) 
Um, the insulation around conductors does not “block” the electric field…
Those wires are supposed by enormous ceramic insulators because that’s what it takes to insulate such high voltages. A rubber coating won’t help at all you if you are unfortunate enough to land on it.
The wires carry AC voltages at different phases. If you touch two wires at once there will be a voltage difference, resulting in current flow through your body.
Generally those were called merely “high lines”.
The weights that are attached to the conductors at the tower ends are vibration dampers,
Under certain weather conditions the lines may “whip” or “dance” and if the action is violent enough ,or lasts long enough, the line can actualy separate or become free from the insulators.
The weights act as counter-weights and prevent,or minimize ,the “dance” effect and resulting stresses.
Those single wires that you see up on the “goatheads” are “static” lines and act to cancel out static charges.
Even if you’re not grounded, if you touch a high voltage line there will be a short current surge as your body charges up to the same voltage level as the line. Several years ago ScientificAmerican ran a story on how electric company workers repair HV transmission lines without getting killed. As the worker approaches the line in his insolated lift bucket, he touches the line with a metal bar that’s wired to the metal frame of the bucket. There is a big spark as the bar, the worker and the bucket charge up to the same level as the line. The bar prevents the first spark from burning the worker’s hand. Once everything’s at the same potential, the worker can touch the line with his hands. ( these guys have GUTS! )
If the parachutist lands on a single line, he’ll probably be greeted by a honk’en big spark. Then he should be OK. However if he comes into contact with two lines or the parachute does and the chute is in anyway conductive, then our hapless adventurer will briefly recreate one of Thomas Edison’s early light bulb experiments.
Yah - I think that the worst situation would be touching two wires with currents flowing in opposite directions. Then you get a current flow and you cook.
But, touching or getting near just one… I don’t know if there would be a spark. Any ideeas?
You wanna talk about guts, check out the guys who do this from a hovering helicopter!
Imagine you have enough current that you need 3 wires to carry it on. Electricity has to make a circuit, so this means you need 3 wires going out and 3 wires coming back, for a grand total of 6 wires. You can save a heck of a lot of wire (which costs money) if you use a little trick. If you stagger the phase of each sine wave in each of the lines by 1/3 of the sine wave cycle, what happens if you add all 3 sine waves together? In case you don’t remember your high school math well enough, the answer is that they add up to zero.
What this means is that if you have 3 equally balanced lines that are 1/3 of a phase apart, you can add them all together and you don’t need any return wires, so you just cut all of your wiring costs in half. You only need the 3 wires going out, and none of the wires coming back.
In reality you never get 3 perfectly balanced lines. Someone somewhere always has to switch on a hair dryer or something that unbalances the load slightly. So, what you end up with is a very thin return wire. You can always tell 3 phase systems because they have 3 big conductors and one small one. The small one is usually connected to earth ground, and is placed above the others for lightning protection.
If you get close to a high voltage line and you are connected to something that is connected to earth (like the tower you just climbed up in order to get to the high voltage line) then the electricity can “arc” from the line to you. Higher voltages can arc farther distances. A lightning bolt is just an arc from the clouds to the ground, but it takes a few million volts to go that far.
Most power lines are not insulated.
Unless you’re in Wisconsin (in the WEPCO service area)…We have a grouded second phase. If you pop open the cover on a 3 phase breaker box, the center phase goes directly to ground, and phase one and phase 3 are 180 degrees apart.
So how do they deal with corrosion?
The part of power lines exposed to the elements is either copper or aluminum, neither of which is much affected by water which the main corrosive agent to which they are exposed. If there is a steel core for structural purposes it is plated with anti-corrosion material
I think you are confusing two phase, 220/110 power with three phase power. In the US the standard residential electric power is produced by a center tapped transformer. The center tap is grounded and the resulting voltages are 110 v. either side of ground and are 180[sup]o[.sup] apart giving 220 volts between the two “hot” wires for electric stoves, clothes dryers etc.
No, it’s three phase. I believe 240V comes in on each side and the B Phase is grounded. So between the A and C Phase, you have 480V and between A and B or B and C we have 240 (which is nice, because we can run 240V appliances off of the three phase and take some of the load off of the single phase box). When I get to work I’ll have to take a look at the wiring and make sure.
I’ve never heard of three phase power in a residence, but then I’ve never lived in the Land of Cheese.
I am familiar with the system Mr. Simmons describes for residential areas.
Ill back Joey up on this one. You can have a 240 OR 480 volt grounded B service. Sometimes called "corner grounded delta". This is NOT common anymore in the Milwaukee area, it is being phased out (heh, heh). I, as an electrician in 494, have run into the grounded B from time to time. The power company originally did this to save on wire. They could run 3 wires everywhere instead of 4. 3 phase 3 wire grounded B,- instead of 3 phase 4 wire. The grounded corner of the delta windings would act as your nuetral, or ground reference, eliminating the need for a fourth wire (nuetral). Hope this helps all!!! P.S. there is also such a monster as a three phase HIGH leg delta, where the windings are grounded between the A and C phase and the B leg is the high leg. Whoever is next can explain this if they want, Im tired.