Comparação do desempenho de técnicas destinadas à detecção de faltas de alta impedância em sistemas de distribuição de energia elétrica

Abstract

In electricity distribution systems, the interruption of the power supply is given by the perfor-mance of the protection system, whether by accident, by atmospheric discharges, by defects in equipment, among others. Conventional protections act whenever they detect an overcurrent in the system, which can be caused by a short circuit, leakage of current in insulators or by over-loading. But there is a situation in which these devices do not work. This occurs when a con-ductor of the primary network ruptures and comes into contact with any surface that has a high electrical resistance. This event is called High Impedance Fault (FAI). Taking into account that these faults are difficult to detect, in this work different methodologies for identifying FAIs in the distribution electric networks are compared, in order to determine, among the analyzed methodologies, which one performs better the function for which it is intended. Three methodologies were selected, and the first method, here called the Envelop method, has a transient detector that is able to classify an FAI through the buildup characteristic of the cur-rent, which is characteristic of this type of fault. The detection of a transient is made based on the calculation of the Euclidean distances between two points in the plane formed by the sam-ples of the current signal and the respective value of the first function-difference of that signal. The second method, however, analyzes the negative sequence current and the signatures re-flected in it by the occurrence of lack of high impedance to ground. Finally, the third method is based on mathematical morphology (MM), which is a non-linear signal processing tool in the time domain. The results obtained demonstrate that both the MM method and that of the negative sequence did not act correctly for all cases analyzed. In contrast, the envelope method was relatively quick and effective for all.