Tony Read 2 Posted November 19, 2009 Share Posted November 19, 2009 This is really a non-aircraft topic, but I need some advice on over-head electricity wires and pylons. National Grid, in their infinite wisdom, want to run a set of 400kv wires with 50m high pylons very close to where I live and fly. As you can imagine, all the villages along the proposed routes (there are four of them) are more than a little miffed. Also models and wires do not mix as I have already found out! Together we are trying to get NG to underground some, if not all of the wires. Of course NG is saying that this is too expensive and this is where you could help. Now, the overhead wires are made of aluminium not much thicker than your finger. The very high transmission voltage helps reduce losses but there is still quite a bit of heat energy given off due to the resistance in the wires. This heat is dissipated into the air. The conductor within underground cables is much, much thicker. Presumably to limit heat generation as it is more difficult to dissipate. Going back to my school days surely these larger cables have less resistance and therefore less energy is wasted? In my simplistic mind there has to be a case for undergrounding cables due to long term economics over short term profits, or am I completely wrong? Edited By Tony Read 2 on 19/11/2009 11:07:45Edited By Tony Read 2 on 19/11/2009 11:08:28 Quote Link to comment Share on other sites More sharing options...
Former Member Posted November 19, 2009 Share Posted November 19, 2009 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
Tony Read 2 Posted November 19, 2009 Author Share Posted November 19, 2009 Fault tracing and lightning strikes are problems associated with underground cables, but nothing that modern technology cannot overcome. As you say, they WILL take the cheapest option, but this may not be in the long term economic good of this country. Quote Link to comment Share on other sites More sharing options...
Tony Cooper Posted November 19, 2009 Share Posted November 19, 2009 How close to your house? if really close they could affect the value, and there have been reported health issues due to the LFreq radiation they give off. Quote Link to comment Share on other sites More sharing options...
Ben Mullins Posted November 19, 2009 Share Posted November 19, 2009 How big would your speed controller have to be to handle 230,000V Quote Link to comment Share on other sites More sharing options...
001 Posted November 19, 2009 Share Posted November 19, 2009 And I thought it was about the pylons on competition free flight models. Are the conductors on the alternative underground cables copper or aluminium? Quote Link to comment Share on other sites More sharing options...
flytilbroke Posted November 19, 2009 Share Posted November 19, 2009 This is similar to many discussions over years throughout the Highlands. Cost is only one factor, possibly a greater factor has been put forward by the Power people. Overhead lines have lower losses than the equivelant underground ones. Quote Link to comment Share on other sites More sharing options...
Andy Gates Posted November 19, 2009 Share Posted November 19, 2009 Ben You would only need a 1 amp esc and a motor with 1kv. That should give you a prop rpm of 230,000. I would be more concerned with the size of the model, unless you were going to fly round the pole models. Quote Link to comment Share on other sites More sharing options...
Chris Card Posted November 19, 2009 Share Posted November 19, 2009 In simplistic terms - to be able to carry the same voltage as an overhead cable, an underground cable would need massively thick insulation. It's a cost and practicality issue and in practice because of the insulation issues the underground cables have to be run at a lower voltage. That means to achieve the same power transmission a higher current is required, which is where the extra losses come in. Air is a good insulator and it's also free. Overhead cables are surrounded by air so they can run a nice high voltage and minmise the current travelling through the cables. QED. Quote Link to comment Share on other sites More sharing options...
Tony Read 2 Posted November 20, 2009 Author Share Posted November 20, 2009 If one route is chosen the wires could pass directly over me. Peevie - the voltage is the same whether the cables are above or below ground - 400kv, but the size of the cable underground is many times that than of those above, and yes there are multiple layers of insulation, and yes it is more expensive - 6 to15 times that of overhead wires. Part of my case for undergrounding would be long term economics as the larger cables must have lower resistances and therefore less losses - but this may not stack up????? There are other issues with overhead wires of course, health, enviromental damage, vulnerability to terrorist attack, susceptibility to ice damage (the Canadian ice storm 10 years ago downed 1000 pylons) etc etc. What this country needs is a 'smart grid' which balances supply and demand across the country but mention this to politicians and their eyes glaze over. Quote Link to comment Share on other sites More sharing options...
Delta Whiskey Posted November 20, 2009 Share Posted November 20, 2009 I would be more worried about the health and loss of value of my property than flying at this stage Tony ! Good luck though....... you need to get all the villagers to stand together to fight this ! Please keep up informed of developments.Edited By Delta Whiskey on 20/11/2009 10:04:23 Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted November 20, 2009 Share Posted November 20, 2009 Tony, hate to be "political" about this, but.... I'm sure you are right, if you were to do a full cost/benefit long term analysis then burying the cable would probably work out cheaper, or only marginally more expensive, for a more visually attractive solution. But... If we wanted people to do those sort of long term calculations then we shouldn't have elected governments over the last 30 years that are obessed with privitisation and the stock market. This is because the stock market's event horizon is the next dividend/agm of the company - which means about the next 12 months! Making long term profit is simply not attractive. So privitised engineering utility companies will always go for the "quick-fix" short-term profit. They have no choice - their is no stock market recognition of social issues or long term profit. I'll get off my soapbox now and put my Kerr Hardy cap back in the cupboard! BEB Quote Link to comment Share on other sites More sharing options...
Tony Read 2 Posted November 20, 2009 Author Share Posted November 20, 2009 BEB - you are SO right! The thing that really annoys me about this new line is that its purpose is to give power to London - not me on the Suffolk/Essex border. I get regular power cuts but the NG lines near by still keep singing! I'm told its to take 3gw from Sizewell C, well the answer is simple - run it round the coast under water and up the Thames estuary, or is that too simple! Quote Link to comment Share on other sites More sharing options...
flytilbroke Posted November 20, 2009 Share Posted November 20, 2009 Might sound strange, I DO agree that we in the UK should have a system in place for MAIN Powerline transmission using the underwater idea. Mainline Spurs, on land "touchdown" points, could be used to transfer power in/out as required. There is after all such a system in place connecting the Continent to England. I doubt as a nation we could afford to do this for anything other than the mainline/s. Therefore we would still have a great deal of overhead lines through-out the land. Aluminium is far from the best material for Electrical power transmission, except for specific purposes. The Plant where I was employed for many years used large "busbars" to power the "cells" producing Aluminium. Even though they were of a substantial diameter/thickness a fair bit of power went in the form of heatloss. Copper is far superior. Millions of tons would be required for the UK alone, for subsurface Power Transmission. Quote Link to comment Share on other sites More sharing options...
001 Posted November 20, 2009 Share Posted November 20, 2009 One problem with putting high tension cables below ground would be that they would probably be installed under roads, across and along them. Think of how many sets go over every major road. We have enough traffic disruption with water, gas, low tension electric, cable tv and telephone lines being dug up. I assume that the six or eight separate cables would have to go into a duct. This would be very big in cross section, then if there was a break, the whole lot would have to be shut down or isolated. Overhead pylons are ugly, but there would seem to be no alternative. Quote Link to comment Share on other sites More sharing options...
Former Member Posted November 21, 2009 Share Posted November 21, 2009 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
Tony Read 2 Posted November 23, 2009 Author Share Posted November 23, 2009 The size of the under ground conductor is MUCH larger than used above ground. Add to this the insulation and you end up with a cross section similar to the diameter of the average coffee mug. NG tell me that to bury the 18 cables of an over head supply would take a trench 50m wide to dissipate heat!!! Or is this a NG exaggeration? I still think under ground distribution has merrits - in some countries this would be the only option. If only we had started out with DC transmission this would not be so much of a problem. Quote Link to comment Share on other sites More sharing options...
Former Member Posted November 23, 2009 Share Posted November 23, 2009 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted November 23, 2009 Share Posted November 23, 2009 I think A/C may also be a lot safer as well as more versatile ? Quote Link to comment Share on other sites More sharing options...
Former Member Posted November 23, 2009 Share Posted November 23, 2009 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted November 23, 2009 Share Posted November 23, 2009 Yes I did ! and yep.... it still bloomin hurts alright - although thankfully its been a few years since I last got zapped Quote Link to comment Share on other sites More sharing options...
Erfolg Posted November 23, 2009 Share Posted November 23, 2009 Underground cable can very expensive especially if oil or gas cooled. A lot of work goes into making them, the conductors are insulated, these are bunched into the conductor shape with the gaps filled with a polymer/rubber strip, the whole lot oversheaved with a insulator/mechanical constraint, plus a lead sheave and armouring etc. In short a big investment of both materials and time. Quote Link to comment Share on other sites More sharing options...
Former Member Posted November 23, 2009 Share Posted November 23, 2009 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
Peter Beeney Posted November 23, 2009 Share Posted November 23, 2009 Regarding the safety differences between AC and DC, I believe that in some cases AC is thought to to make the muscles contract. Thus if you are gripping a wire, say, you may not be able to let go. On the other hand, it is said, sometimes it can ‘throw you off’. In general terms, just a few milli-amps of current can be lethal, which is why it is difficult to get the safety circuit breakers just right. Although some people do seem to have a very high natural body resistance, I’ve seen reliable evidence of that! Regarding the pylons, I think the underground system is getting closer. I believe there are 400kv underground lines running, one such is about 10 miles long, in a 3ft diameter tunnel. The cables now use a very high temperature plastic insulation, and with management systems like temperature monitoring the cable can, if necessary, be grossly overloaded for short periods. Yet another case where a thermometer doubles up as an ammeter, perhaps? The tunnel is about 20 metres below the surface, sometimes much deeper, with a monorail system for maintenance and inspection; and enough space for another cable if it’s ever required. One advantage of such an arrangement is that the maintenance is very low. Some systems do use DC, the power swap arrangements with the French, under the English Channel, is HVDC. There are inverters at either end to convert it back to AC. If a really cost efficient way of boring suitable tunnels evolves, and I’m sure it eventually will, then maybe many more power cables will go under ground. PB Quote Link to comment Share on other sites More sharing options...
Former Member Posted November 24, 2009 Share Posted November 24, 2009 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
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