Sistema de avaliação do nível de degradação de para-raios de óxido de zinco.

Abstract

The zinc oxide (ZnO) surge arresters are equipments used in the electrical power system protection and have been employed in the least 30 years with the objective of increase the reliability of the electrical system as a whole. The ZnO based surge arresters are formed by varistors, elements that present high non-linearity characteristic between the applied voltage and the current. The main function of the ZnO surge arresters is to protect the electrical system against lightning discharges or electrical system discharges caused by transmission lines switching. Nowadays, several techniques were developed for the ZnO surge arrester monitoring, but does not exist a standard about the best technique that should be used, each technique presents advantages and disadvantages. Other problem commonly found using these techniques is that does not exist a posterior data analysis to identify and to classify the possible problems detected during the monitoring. One of the most used techniques in the ZnO surge degradation level monitoring is the leakage current measurement. This current is one of the most reliable information about its integrity condition or degradation. The leakage current monitoring of a ZnO surge arrester in operation can indicate permanent imperfections or transient behavior (problems) of the surge arrester. In this work, a wireless monitoring system of the ZnO surge arrester degradation level based on the leakage current measurement and its harmonic analysis is presented. For the measurement of the leakage current, the system uses an inductive no-invasive sensor based on high permeability alloys. The proposed methodology is composed of the following procedures: the ZnO surge arrester leakage current measurement, total leakage current decomposition in the capacitive and resistive components and the third harmonic component calculation. The obtained data are send for the substation control room using a wireless communication system based on the ZigBee communication protocol operating in the frequency of 2,4 GHz.