Simulation and measurement of S parameter in UHF band of GIS
The gas-insulated switchgear (GIS) is widely used as the main power equipment in electric power system due to its high reliability and compactness. The insulation breakdown of GIS are usually started from partial discharge (PD), which is caused by the aging of insulating materials or the defects during manufacture and operation. Based on discharge mechanism and secondary physical phenomena accompanying with PD in GIS, many kinds of methods for detecting PD have been developed in past half century. In recent years, the ultra-high frequency (UHF) method by using the internal or external UHF sensors to detect the electromagnetic (EM) waves radiated from PD, has been presented as a promising method to diagnose the insulation system of GIS.
By varying the PD source position or UHF sensor location, the influence of GIS structure and PD location on the propagation characteristics of EM waves in GIS have been studied by many researchers. In this paper, by using the two-port network theory, GIS with two UHF sensors are considered as the two-port network system. Therefore, the S parameters between two UHF sensors can be described as the propagation characteristics of the GIS structure between these two UHF sensors, which represents the refraction and reflection relationship of EM waves.
First, by employing the finite integration technique, the simulation of S parameters is performed to analyze changes of S parameters with the number of basin-type insulators. The attenuation influence of one insulator can be up to -3dB, which is in proportion to the number of insulators. In addition, a 252kV GIS experiment platform is established, where signals from different positions could be obtained by inner sensors. Compared with S parameters calculated from experiment, the simulation results show a good consistency both in waveform and amplitude, which is proven to be reasonable. Moreover, a vector network analyzer is used to measure S parameters in different structures of GIS, and simulation models are refined and changed. The results of vector network analyzer are compared with ones of simulation which have a good consistency and prove the rationalisation of the simulation conclusion.
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