Novo método para monitoramento e localização de fontes de descargas parciais em transformadores de potência utilizando medições e simulações UHF.

Abstract

This research presents a method for monitoring and location of partial discharges (PD) sour- ces in power transformers based on the electromagnetic waves radiated by the PD pulse. Two contributions are presented. The first one is the development of a UHF sensor for PD measu- rement through adaptation on dielectric windows of power transformers. For this purpose, a bio-inspired microstrip antenna was designed with the ground plane truncated along the length of the transmission line. The shape of the patch antenna was based on the leaf of the Jatropha mollissima (Pohl) Baill plant. Thus, an increase of the bandwidth was obtained with a reduction in the antenna area within the dimensions required for the installation in the dielectric window of power transformers. Then, the microstrip antenna was encapsulated in epoxy resins with a thickness of 20 mm to provide protection against corrosion, mechanical support, and a lifetime compatibility with power transformers. Besides that, an aluminum enclosure was produced to protect against external interference and allow the sensor to be attached on the power transfor- mer tank. In order to verify the electrical parameters of the developed sensor, measurements of the gain and the reflection coefficient were performed in an anechoic chamber. Lastly, the antenna sensitivity for PD detection was compared with the IEC 60270 standard method. For this purpose, simultaneous tests were carried out in a PD generator setup, composed of an oil cell with needle-plane electrodes. In this way, PD signals were produced with values similar to those that could be generated in real transformers. The second contribution of this thesis is the proposition of an algorithm for the location of the PD sources in power transformers. The algorithm proposed in this work is more accurate than the existing methods because it con- templates the effects of the reflection, refractions and diffractions that the UHF signal suffers within the equipment tank. The method uses computational simulations of the electromagnetic waves generated by PD, obtaining the time delay of the signal from each point in the three- dimensional space until the UHF sensors. The signals calculated computationally are compared with the signals measured in the field, so that the indicated position for the PD source is that the simulated propagation delay best approaches the measured data. The equations of the method are defined as a three-dimensional optimization problem, so that the particle swarm optimiza- tion algorithm was used. The experimental tests demonstrated the effectiveness of the sensor for detection of PD signals with apparent charge values higher than 35 Pc. The sensor pre- sented a final dimension of 260 x 260 x 150 mm and bandwidth of 772 MHz to 1272 MHz.It was also tested the PD source localization algorithm and demonstrated its effectiveness in a computational environment.