Underground distribution hybrid system

The "network" system in underground distribution applied in several areas of Eletropaulo and is constituted by secondary nets in mesh, supplied by radial feeders and protected by breakers of low voltage(LV), with directional relay, coupled to each transformer, whose basic function is interrupting the feeding of primary net failures for inverse power flow comes from secondary net. Although it offers high reliability degree, configuration net presents a high cost for counting with great reservation transformers capacity and MV/LV net, beyond of protection devices mentioned — "network protector" — whose cost is also very high. Looking for solutions to improve the efficiency and the cost of their installations, Eletropaulo and Enerq/EPUSP developed a study, related in this article, where they are proposed and analyzed configurations alternatives deriving from configuration "network", without of the network protector and can be applied gradually and regarding radially secundary net, conventional protections and use in underground primary switch transfer automatically, the transformer feeding when primary fails. The application of the results obtained is presented in a pilot net located at the old downtown of Sao Paulo's city. The studies and researches form developed in the extent of the Program of Research and Technological Development of Eletropaulo — Cycle 2001/2002 — entitled “Hybrid development patterns for underground nets”.