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Thursday, June 19, 2014

Old Technology

We see them blighting the countryside everywhere. Pylons and overhead power-lines carrying power for the electricity national grid. A necessary and unavoidable evil some say. But it needn’t be and hasn’t been for over 50 years.

  Gas Insulated Lines (or GI)  are reliable, efficient, high capacity underground electricity transmission. Patents for GIL have been held since the 1960’s and in Germany, engineering giant Siemens has had a system running beneath the black forest for over 30 years. And in all that time it has run faultlessly, exhibiting no degradation. The first American GIL installation in New Jersey in 1972. So GIL is not a new technology.

GIL is an essentially simple technology. A long while ago, it was discovered that the majority of the energy flowing in a high capacity transmission cable actually flows through the outer part of the conductor. So if you don’t need the core of the conductor, why have one? GIL is in fact a tube within a tube. The inner one conducts the electricity, the outer contains the insulating gas. The two are kept apart using epoxy spacers. Once assembled, the sections of GIL that form a complete transmission system are filled with a pressurised mixture of gasses, 80% nitrogen (which you are surrounded by right now) and 20% sulphur hexafloride. This last gas is a greenhouse gas and so stringent precautions are taken to prevent leakage. Assembly of GIL  involves bringing lengths of the aluminium components to site and flawlessly welding them together using fully automated welding machines that X-ray the weld continuously to test for weld quality.

GIL can be installed in a number of ways which include direct burial and wall mounting in a tunnel. GIL can be installed in a number of ways which include direct burial and wall mounting in a tunnel . Whilst direct burial has been done in Europe, tunnel mounting brings benefits of serviceability and upgradability. This is because GIL has the enormous benefit of giving out very low heat and electromagnetic emissions compared with cables. In turn, this allows GIL to be racked close together on tunnel walls. If you need to increase capacity, you simply add more GIL lines into the tunnel. And because the emissions are low, engineers can service one GIL while all the others are live. This is not possible with underground cable transmission systems.

 GIL has a very low environmental impact compared to other transmission methods. GIL can be installed in a 4m wide tunnel, cables need a 60m wide swathe of land to do the same job. GIL emits little heat or electromagnetic radiation
   
Another example of capitalism cost-cutting holding back progress.

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