Undergrounding
In civil engineering, undergrounding is the replacement of overhead cables providing electrical power or telecommunications, with underground cables. It demonstrates the higher technology in developed countries for fire prevention and to make the power lines less susceptible to outages during high wind thunderstorms or heavy snow or ice storms. An added benefit of undergrounding is the aesthetic quality of the landscape without the powerlines. Undergrounding can increase the initial costs of electric power transmission and distribution but may decrease operational costs over the lifetime of the cables. History. The first uses of undergrounding had a basis in the detonation  of mining explosives and in undersea telegraph cables. Electric cables were used in Russia to detonate mining explosives in 1812, and to carry telegraph signals across the English Channel in 1850. With the spread of early electrical power systems, undergrounding began to increase as well. Thomas Edison used underground DC “street pipes” in his early distribution networks; they were insulated first with jute in 1880, before progressing to rubber insulation in 1882. Subsequent developments occurred in both insulation and fabrication techniques: During the 20th century direct-buried cable became commonplace. Comparison. The aerial cables that carry high-voltage electricity and  are supported by large pylons are generally considered an unattractive feature of the countryside. Underground cables can transmit power across densely populated areas or areas where land is costly or environmentally or aesthetically sensitive. Underground and underwater crossings may be a practical alternative for crossing rivers. Disadvantages. The advantages can in some cases outweigh the disadvantages of the higher investment cost, and more expensive maintenance and management. Regulations. Europe. The UK regulator Office of Gas and Electricity Markets (OFGEM) permits transmission companies to recoup the cost of some undergrounding in their prices to consumers. The undergrounding must be in National  Parks or designated Areas of Outstanding Natural Beauty (AONB) to qualify. In 2021 work started on a project to bury of 400kV overhead power lines running from near Winterbourne Abbas to Friar Waddon (, north-west of Weymouth) in Dorset AONB. Similar schemes are planned for Snowdonia, the Peak District and the North Wessex Downs. The most visually intrusive overhead cables of the core transmission network are excluded from the scheme. Some undergrounding projects are funded by the proceeds of national lottery. All low and medium voltage electrical power (<50 kV) in the Netherlands is now supplied underground. In Germany , 73% of the medium voltage cables are underground and 87% of low voltage cables are underground. The high percentage of underground cables contributes to the very high grid reliability (SAIDI < 20). In comparison, the SAIDI value (minutes without electricity per year) in the Netherlands is about 30, and in the UK it is about 70. California. In the United States, the California Public Utilities Commission (CPUC) Rule 20 permits the undergrounding of electrical power cables under certain situations. Rule 20A projects are paid for by all customers of the utility companies. Rule 20B projects are partially funded this way  and cover the cost of an equivalent overhead system. Rule 20C projects enable property owners to fund the undergrounding. Japan. Most electrical power in Japan is still distributed by aerial cables. In Tokyo's 23 wards, according to Japan's Construction and Transport Ministry, just 7.3 percent of cables were laid underground as of March 2008. Variants. A compromise between undergrounding and using overhead lines is installing air cables. Aerial cables are insulated cables spun between poles and used for power transmission or telecommunication services. An advantage of aerial cables is that their insulation removes the danger of electric shock  (unless the cables are damaged). Another advantage is that they forgo the costs—particularly high in rocky areas—of burying. The disadvantages of aerial cables are that they have the same aesthetic issues as standard overhead lines and that they can be affected by storms. However, if the insulation is not destroyed during pylon failure or when hit by a tree, there is no interruption of service. Electrical hazards are minimised and re-hanging the cables may be possible without power interruption.