Faltas de alta impedância: detecção e localização de rompimento de condutores em circuito primário de redes aéreas de distribuição baseado em desequilibrio de tensão

Abstract

The breakage of energized conductors of distribution aerial networks (RDA) in the event of phase-conductors contacting the soil through high values of fault impedances represents a serious risk of fire and a threat to human lives. The conventional overcurrent protection devices usually involves significant limitations concerning detection of this nature of fault since these devices are not sensitive to values of current that are bellow or very close to load currents. Several methods and equipment have been proposed in order to solve this problem since 1970s. Despite studies have been providing a better understanding of the problem and despite the increase of the probabilities of detecting these faults, the mentioned methods do not involve enough confidence and security in terms of fault detection. Besides, in these methods the protection system alone is not able to locate the fault in the substation by itself. However some recent studies propose the detection of broken conductors by means of voltage unbalance. The method recommends the installation of sensors at strategic points of the feeder, which detect the voltage unbalance caused by broken conductors taking the zero-sequence voltage as the monitoring parameter. Among the advantages of this method it can be mentioned its reliability and security with respect to the detection of this nature of faults, no matter which is the dynamic of the conductor towards soil surface or the value and the randomness of the fault current or even the point of the conductor rupture (load or source side of the line). In this way, an algorithm for phase-fault location in distribution feeders is proposed in this work. The algorithm focus on the protection against the rupture and drop of energized primary conductors under high impedance fault condition in such a way that the Distribution Operation Center (COD) may promptly interfere. The algorithm involves a route logic of distribution networks for non-directional bars. It were performed several simulations using Alternative Transients Program (ATP) including the modeling of a real CEMIGs feeder. A program developed in MatLab® language was used in order to locate the faults. In all cases, the algorithm indicated correctly the location of faults. In addition to the localization of this kind of fault and taking into account the required protection level, the method is able to make difference between a broken conductor and a single phase trip of the protection equipment (a fuse-link melting, for example) locating the fault immediately after it occurs. This will reduce the time delay to restore the energy supply for both kinds of faults, besides providing a higher security level for people in case of occurrence of high impedance faults caused by rupture of the primary conductors of the feeder.