Técnica de ajuste adapativo para relés de distância sob condição de saturação dos transformadores de corrente

Abstract

The protection of transmission lines (TLs) is done by relays. Among these devices, the distance relay is characterized by the measuring of the impedance up to the fault point. This measurement is taken from the voltage and current signals from the network, which are obtained from the potential (PT) and current (CT) transformers, respectively. These transformers are designed to replicate these signals as closely as possible, enabling proper operation of the protective relays connected in their secondary terminals. However, current transformers are subject to the core saturation, which causes distortions in the waveform of the current signals received by the protection relays, which may affect its operations. This paper proposes a technique of adaptive adjustment for distance relays to avoid performance problems resulting from the saturation of the current transformers upon the occurrence of a fault in a transmission line. Situations considering different levels of remaining flux in CT core and different types of fault were analyzed. For this, a test system was used to simulate a transmission line in EMTP-ATP®, from which the voltage and current signals were obtained to be used in the study. The logic of the relay and the proposed methodology were implemented in MATLAB®. A preliminary study regarding the performance of the relay submitted to the CT saturation was conducted to determine the problems of under or overreach presented by this dispositive. This study served as a comparison parameter for determining the performance of the proposed technique, which aims to automatically adjust the distance relay maximum torque angle in the moment when the CT saturation is detected, thus eliminating any delay in the operation, underreach or overreaching problems caused by this phenomenon. Finally, the results obtained show that the technique is effective and robust, providing large improvement in the performance of distance relays operating under CT saturation condition.