Utilização de um sensor de campo 3D e métodos estatísticos para diagnóstico de isoladores.

Abstract

The insulating performance of four transmission lines subjected to 12 kV were evaluated considering the chemical pollution of the insulator which has undergone. A system of data acquisition and processing was mounted to enable the classification of the level of contamination, to identify the best frequency band containing the spectral signature of the insulators and investigate polarization which is more suitable for measurements using a statistical approach . When subjected to high voltages, the insulator radiate radio frequency signals due to the corona effect. Statistical methods such as histograms, test normality and the correlation coefficient were used to rate the level of pollution in glass insulators. It is shown that in certain situations the histograms can be used to distinguish the condition of the insulators. By using the correlation coefficient in conjunction with the normality test can be identified frequency bands of interest, or bands where the spectral signature is the insulators. Tests were limited to a band of 300 MHz (30 MHz to 330 MHz), for use higher bands excessively increases the time required for data acquisition. Two types of antennas were used: biconical and isotropic (3D sensor). During measurements with the biconical antenna, two types of polarization were used, the vertical and horizontal polarization. The choice of antenna (biconical) with one type of polarization does not consider the signals present in the other polarization, causing loss of relevant information of the signal radiated by insulators. To investigate this problem an antenna with special features was used. This is the 3D sensor (isotropic antenna) that captures the radiated signal by insulators in polarizations based on the three, providing a single electric field vector that summarizes the overall bias incident. Measurements with 3D sensor were compared with measurements made with the linear antenna, in order to find what polarization leads to a better match with the polarization of the radiated signal by insulators.