Supplying small loads at reasonable cost

The hundreds of kilometres of power lines that stretch from Brazil's under-developed areas to its big urban centers bypass many small, electricity-less towns. Excluded from the mainstream of development, their inhabitants leave en-masse for the already overpopulated cities. Eletronorte decided to find a way to improve matters. It undertook a pioneering engineering project to supply electricity to communities along and near the routes of 230-kV transmission lines. The shield-wire lines (SWL) project, as it is called, is straight forward. A symmetrical three-phase voltage system, formed of a transmission line's two shield wires and earth, delivers reliable power to small communities along the line. The idea is to use simple balancing components to derive the symmetrical three-phase voltage system. The components are a series resistor and inductor (reactor) in the earth path, plus a capacitor branched between the two shield wires.