| Gas insulated switchgear (GIS) is more and more widely used in the power system because of its compact structure, not affected by the external environment, smaller size, long maintenance cycle and high reliability. So the on-line partial discharge monitoring for GIS is of great significance. Among them, ultra high frequency (UHF) on-line monitoring method has been gradually extended in the field of GIS partial discharge on-line monitoring. But due to the electromagnetic environment of partial discharge on-line monitoring is very complex and The weak partial discharge signals are always overwhelmed by interference in GIS partial discharge online monitoring. Therefore, how to effectively suppress interference plays an important part in GIS partial discharge online monitoring.Anti interference of GIS partial discharge online monitoring system based on ultra high frequency method is the research object in this paper. Based on filtering the periodic narrowband interference by using Fourier series filtering algorithm, the lifting dual-tree complex wavelet transform is put forward into the anti interference research because of the disadvantages of the first generation wavelet denoising algorithm. This algorithm is obtained by lifting the first generation dual-tree complex wavelet transform. And it combines the excellent denoising ability of complex wavelet transform and the high calculation efficiency of lifting wavelet transform. Then the online monitoring soft software system uses this algorithm as the core of calculation module to do field monitoring experiment. The main research contents and achievements are as follows:(1) Firstly, the common insulation defects and typical partial discharge types in GIS are summarized, and the mechanism of partial discharge in GIS is analyzed. Then, the electromagnetic wave equation of GIS equivalent coaxial waveguide system is derived, and the propagation characteristics of electromagnetic wave in GIS are analyzed. Finally, the propagation and attenuation of electromagnetic wave in GIS are analyzed qualitatively by means of partial discharge simulation in GIS based on HFSS Ansoft software.(2) The design process and system performance of the hardware and software system of GIS partial discharge on-line monitoring system based on ultra high frequency method are analyzed. And the characteristics of the interference in the monitoring field are analyzed. It is determined that the system has the potential to collect the interference signal, including the frequency of 900MHz radio signal and white-noise interference.(3) The periodic narrowband interference is filtered out by using Fourier series filtering algorithm. And in order to suppress white-noise more efficiently, the lifting dual-tree complex wavelet transform is put forward into the white-noise suppression research. Then the performance of the lifting dual-tree complex wavelet algorithm is assessed by the operation efficiency and the denoising effect. The results show that the lifting dual-tree complex wavelet transform has quick calculation speed,takes less computer memory, can quickly and efficiently filter out white-noise.(4) In order to verify the effectiveness of the proposed denoising algorithm, the monitoring system is tested in the GIS experimental platform. Experimental results show that the denoising algorithm based on Fourier series filtering and lifting dual-tree complex wavelet can effectively suppress the interference of the monitoring system, and the data processing results can accurately characterize the GIS internal partial discharge status. Compared with other denoising algorithms, it can better meet the the requirements of real-time in GIS partial discharge online monitoring, and has higher application value in the engineering practice. |
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