Thread Number: 76032  /  Tag: Other Home Products or Autos
Power line aficiandos - what is this on these poles? Why was it designed that way?
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Post# 998857   6/30/2018 at 02:54 by superocd (PNW)        

South of my hometown in rural MO there is a three-phase, ~60kV secondary distribution line, running alongside the highway for some distance until it deviates east to a substation. I think the original poles in this run are about 50-60 years old. There are a few replacement poles due to storm damage, but it's still quite impressive that most of the original poles still stand this day considering that tornadoes have a tendency of touching down in that area and high winds are certainly not uncommon.

One thing I never could understand about these poles is that the middle insulator (circled) doesn't just sit on the top of the pole. Instead, there are two vertical boards surrounding each side of the insulator mount. In the space between the boards, there are what looks like two metallic bars bent into a "V" tipped on its side. It would almost look like a cutout or recloser but this is on EVERY pole and the other two conductors on the crossarm does not have this, as you can see on the picture. I've circled the object of my question. I'm doubtful it's a lighting arrestor because the replacement poles do not have any such thing; and on these poles, the other two conductors are not equipped with them.

I'm taking a road trip down there to visit my folks this fall. Maybe I could catch one of the utility guys while I'm in town and ask them, but I'm wondering if anyone here knows what this is and why they designed it that way.

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Post# 998862 , Reply# 1   6/30/2018 at 04:53 by Rolls_rapide (Scotland, UK)        

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Could it be an earthing wire? That it appears to connect to the metalwork of the pylon support would suggest so.

Post# 998863 , Reply# 2   6/30/2018 at 05:04 by Rolls_rapide (Scotland, UK)        

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Scroll down this Wikipaedia page to "Ground Wires".


Post# 998865 , Reply# 3   6/30/2018 at 06:16 by tolivac (greenville nc)        

These shots of the pole equipment are something I haven't seen.The 69Kv lines I had seen had the shield cables above them-and some of them ran short distance underground.Was a PEPCO installation near the radio transmitter site I used to work at.Next door to the site is a 69Kv to 13 KV substation.The station had its own dedicagted feeder!
At the VOA site the 115Kv 3 Ph feeders have the two shield cables above the hot lines.For grounding usually ALL 3 phases are grounded if the linemen have to work on them after the section has been shut down and grounded.As you would know-like our antenna structures the cables can pick up voltages from adjacent lines or from the air like antennas.We get was is called "Hot Tag notice" when the power company lineman have to work on our 115Kv line feeder.Replacing the pylons.They have us shut down our generator so it cannot possibly feed back into the lines.Remember our substation transformers can conduct backward-so the reason we shut down our genset.They call in the morning when they want the generator disabled.Then I go out and shut off its control switch.
But back to your lines-maybe you can contact the power company there-often they can tell you about their equipment-or ask a lineman if you see one and show interest in the work.They usually like to tell you.I wonder about that center device,too!Want to know the mystery.

Post# 998881 , Reply# 4   6/30/2018 at 09:52 by norgeway (mocksville n c )        
One thing for sure

If you touched that line , you would be a instant cinder! BAM!

Post# 998916 , Reply# 5   6/30/2018 at 18:17 by iej (Ireland)        

That's a fairly simple single phase, 2-wire medium voltage line with a 'sky wire' or 'overhead ground/earth wire' on top. They're a just grounded conductor that is used to protect against lightening strikes.

They typically shield at an angle of about 30ļ either side of the wire, so protect the power carrying conductors below.

I'm not sure what voltage that would run at in the US. Network distribution and transmission voltages vary from country-to-country in Europe too, but I'm not sure what the voltages used in the US networks are.

In Ireland for example we use:

Low Voltage Distribution:
230/400V (50Hz) (3-phase with grounded neutral)

10kV (old rural standard - largely phased out)
20kV (rural)
38kV (mostly urban)

110kV (original 1920s grid standard)

Grid-to-Grid interconnection:
Ī200 kV DC

Post# 998925 , Reply# 6   6/30/2018 at 20:51 by superocd (PNW)        

@iej - I almost thought it was an overhead ground wire due to the proximity of the metallic piece bent outwards and "gapped" a few inches from that specific line, but the gauge of the middle conductor appears the same as the gauge of the conductors on the crossarm and the insulator on the middle conductor. Both would be overkill for an OGW, which led me to believe that this is a current carrying conductor along with the conductors on the crossarm.

I'm also confused because this run feeds a smaller substation eastward. That substation reduces the power to three phase ~20kV for last-mile distribution (and a few SWER lines [single wire earth return] from those too for the real remote areas and for the older farms out there that can make do with single-phase power).

The output of the substation that it feeds (and it's the sole feeder line to that substation) is three-phase for last-mile distribution. I have a screenshot from Google Maps street view of that substation (last picture). It's kind of fuzzy though because this was "street viewed" before Google had HD cameras on their street view cars. Each of those three conductors coming off the last pole passed through the switch and the transformer.

The other lines in the county just have a simple OGW at the very top along with its three phase conductor set, as you can see in the first four pictures.

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Post# 998932 , Reply# 7   6/30/2018 at 22:13 by DADoES (TX,†U.S. of A.)        

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RJ says:† "It's probably a way to retrofit the pole construction to protect raptors.† It physically separates the conductors further so that a large bird can't touch 2 wires at the same time."

Post# 998935 , Reply# 8   6/30/2018 at 22:44 by wayupnorth (On a lake between Bangor and Bar Harbor)        

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Top of the poles are always power and the bottom lines were from the phone company and cable.

Post# 998951 , Reply# 9   7/1/2018 at 02:28 by RP2813 (The Big Blue Bubble)        
Photo 2 of 5

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That configuration has always reminded me of Shirley Temple.

Post# 999010 , Reply# 10   7/1/2018 at 17:57 by iej (Ireland)        

Historically in Ireland the power company has never allowed any other utilityís wiring on their poles. Telephone lines were always carried on their own poles and cable television usually goes underground or, where it was laid back in the 1960 and 70s, the wiring usually runs house to house from the nearest amp with the taps on the eves / soffits.

We tend to have a lot more of our local power lines underground than youíd see in the US. Thereís some use of overhead distribution in towns and cities but itís avoided where possible.

Rural services would tend to be overhead to the edge of the site in modern installations and underground from threre or; in older installations aerial wires are used connecting direct to the building.

The only use of power company ducts and lines for telecommunications is a joint venture company called Siro. Itís owned 50% by ESB Networks, the state owned utility that operates the electricity network. It provides fiber to home access but doesnít sell it directly. So you order a service from a range of ISPs as itís delivered over that fiber infrastructure. So basically itís just publicly owned fiber pathways to homes and you can shop around and use whoever you want for your internet, phone and TV services.

That competes with another wholesale FTTC (up to 250Mbit/s with super-vectoring) and FTTH (gigabit) network owned by the largest telco OpenEir and also with cable from Virgin Media (Liberty Global / UPC) that currently delivers 360mbit/s.

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