Type of Transmission System

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infinity

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Does anyone know what type of transmission system this is? I recently took this photo while on the US/Canadian border. These power lines are thought to originate at a hydroelectric plant along the Connecticut river in New Hampshire and go deep into Quebec. Seems strange to me have two groups of three conductors each and one single conductor.

Powerlines%2010.17.08.jpg
 
Those darn conductor thieves are at it again! :grin:

Well, it?s not 3-phase, as the third phase is obviously missing. I believe it would not be a DC transmission line either. I base that on the suspicion (all I can handle before I finish my coffee) that DC lines do not suffer ?corona losses,? and thus would not benefit from bundling of conductors. So I am left to conclude it is a single phase system. But I have never heard of transmitting single phase over towers that big.
 
Yeah, those towers must be at least 75' tall. Judging from the number of rings on those insulators I would guess that the voltage is quite high.
 
I think that it is high voltage DC.
The multiple conductors on each side of the towers may have been to utilise standard conductor sizes, or to reduce corona losses, I dont think that DC is immune to such losses.

The third single conductor, on much smaller insulators, may be a neutral for the DC system, this would be at relativly close to ground potential and thus not need long insulators.
High voltage DC systems normally operate with the same current in the postive and negative conductors, with no current in the neutral.

In event that the converting plant fails at one end of a HVDC line, then pending repairs it is sometimes possible to resume service at half capacity, useing one half of the convertor, and one only of the high voltage cables, with the return current via the neutral.
 
More pictures, I think

More pictures, I think

I think those lines may originate at the Commerford Dam Power Station in Monroe, NH. They run over family property up there. I was just there a couple weeks ago.

There are great views on Google Earth-search: Dam rd Monroe, nh, click on the little blue blocks at Commerford. In the pictures the lines look about the same (not sure if the smaller center conducter is there?). The lines all head north.
 
charlie b said:
Those darn conductor thieves are at it again! :grin:

Well, it?s not 3-phase, as the third phase is obviously missing. I believe it would not be a DC transmission line either. I base that on the suspicion (all I can handle before I finish my coffee) that DC lines do not suffer ?corona losses,? and thus would not benefit from bundling of conductors. So I am left to conclude it is a single phase system. But I have never heard of transmitting single phase over towers that big.
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The three conductors per leg of the DC would give a larger surface area, better cooling, thus save on conductor costs.
Maybe that's why it's configured that way.
 
Very interesting high voltage DC transmission. Thomas Edison would be proud. :wink: Thanks guys.
 
From the lengths of the insulators it looks like they are rated for 550kv. Those conductor are atleast 1400Kcmil Al if not larger
 
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Deffo HVDC, and based on the location description I think it is this line 450KV, 2GW.

HVDC is facinating technology that has been around a long time, have a look at this Wikipedia article.

I got interested in HVDC as what was the worlds biggest HVDC project when it was built in 1965 goes just outside my township, I drive under it every day.

Basically one pole line is positive with respect to ground, and the other negative. The return line in the centre above the pole conductors is in parallel with the ground path, and generally the return line is insulated to 33KV...
 
HVDC has two main uses, firstly transmission of a lot of power over a long distance. The reason for this is losses are much lower because there are no capacitive losses. This is even more the case if the conductors are underground or under water.

HVDC is expensive to comission, because of the cost of the converter stations at each end, so there is a tradeoff between distance, losses and cost. But the transmission lines are cheaper as there is less conductors (two versus the normal six on a double circuit AC tower) and thus less tower metal.

Secondly, one can use "back to back" HVDC to connect together grids that are not syncronised. "Back to back" means no intervening DC wire, its just two converter stations in one location, with AC in and out. You do a lot of that in the USA, you have (I believe) five unsyncronised grids, all of which transfer power between them using back to back HVDC. Also Japan, they have both 50Hz and 60Hz grids in one country, so they are obviously unsyncronised!

Sometimes both these reasons apply, for example there is a submarine link between the UK and France so its an undersea long cable, and the grids of the two countries are unsyncronised.
 
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As I understand it there are 3 grids in the US and not a lot of power is transfered from grid to grid...at least not a lot when compared to the power used in any one of the grids. The grids are east of the rockies, west of the rockies, and Texas.
 
don_resqcapt19 said:
As I understand it there are 3 grids in the US and not a lot of power is transfered from grid to grid...at least not a lot when compared to the power used in any one of the grids. The grids are east of the rockies, west of the rockies, and Texas.
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When I was a young engineer I worked for a POCO called Public Service Co of Oklahoma which was owned by Central & Southwest (Now called AEP) as a sub-station engineer.

Anyway CSW owned several utilities in TX and we designed a HVDC interconnect with a couple of sister POCO's in TX. It was a bit strange because the HVDS path was only a matter of a few feet in length. Tx is the only state (or at least I think it is) that is not connected to the national grid, and the only legal way to interconnect accross state lines is via HVDC
 
dbuckley said:
Also Japan, they have both 50Hz and 60Hz grids in one country, so they are obviously unsyncronised!
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Well, they're in synch every so often, just like the broken clock that's still right twice a day.
 
dbuckley said:
Also Japan, they have both 50Hz and 60Hz grids in one country, so they are obviously unsyncronised!
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Itaipu is such a scheme that runs between Paraguay and Brazil.
50-60Hz, about 800km and, with 2 x 3150MW systems, possibly the largest in the world.
dbuckley said:
Sometimes both these reasons apply, for example there is a submarine link between the UK and France so its an undersea long cable, and the grids of the two countries are unsyncronised.
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There's another submarine link under construction. It's the BritNed link and will be between UK and Netherlands. At 1000MW, It won't be as large as the Cross Channel HVDC link but much longer - about 260 km.
But, at 580 km, the NorNed, Norway to Netherlands link claims the longest HVDC submarine cable.
http://kn.theiet.org/magazine/issues/0817/news.cfm
 
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