Development Of Surface Discharge Model And External UHF Sensor

The UHF PD(Partial Discharge) measurement technique has been extensively employed in recent decades due to its high sensitivity, noise immunity, broad effective detection range and the ability to both locate and identify the defects, In this paper, the author carried on his research on the PD model, the propagation characteristic of UHF signals through resin sprues of GIS and the development of external UHF sensor, aiming at solving some key problems and providing some technical supports for the standardization and establishment of calibration of GIS PD detection system.In the dissertation, in the light of the mechanism of surface discharge in GIS, the author proposed and developed a PD model with unique structure, which we called the“Needle-Sphere” surface discharge model. After tested both in the air environment in laboratory and the SF6 environment in GIS, it proved to be able to discharge stably on a large voltage scale(under low barometric pressure) with a small discharge quantity and rather good repeatability.Currently, lots of the research about the propagation of UHF signals focus on the cavity of GIS instead of the sprue on insulators. In the thesis, by dint of experiments and simulations, the author drew some conclusions about the UHF signals on the surface of the resin spure: the electric field parallels to the sprue’s short edge; the intensity of the signals released from the resin sprue mainly depends on the length of its long edge; with length of its long edge increasing, the intensity of UHF signals enhances first and weakens later and get its maximum on 75 mm when the PD source is metal protrusion or free metallic particles, while when the PD is resulted from surface discharge, the the intensity of UHF signals will strengthen as long as the length of resin sprue’s long edge increases.Based on the propagation characteristic of UHF signals through resin sprues, theauthor developed 3 kinds of UHF sensors: bowtie slot antenna, half-ellipse antenna and half-circle antenna. With simulation calculations, some parameters of the sensors like VSWR, radiation pattern, far filed gain and effective height were obtained, which were quite pleased in terms of the design request. The tests of these sensors both in open free space and GIS platform showed that the performance of half-ellipse antenna and half-circle antenna both in time and frequency domain were much better than 2 sensors which had been adopted in power system, which means the half-ellipse antenna and half-circle antenna proposed in this paper can be applied in GIS PD detection.