Research on covered medium-voltage overhead lines in Finland

The use of plastic-covered conductors on medium-voltage power lines has considerably reduced the space required compared with conventional overhead lines. In addition, disruptions in electrical power distribution have been reduced, since, thanks to the insulating covering, conductors have withstood such things as overvoltages due to clashes and, for a certain period, the pressure of a fallen tree on the line. The Finnish 20 kV SAX-system, which has been installed in Finland since 1984, belongs to this category of covered overhead lines. Research was carried out into the suitability of this type of line for forest areas in 1987 and 1988 using a comprehensive test series. The tests simulated the situations in which trees most often caused damage to present 20 kV overhead lines