| Partial discharge (PD) in Gas Insulated Switchgear (GIS) is one of the important factors for arising the fault, and therefore the on-line monitoring PD in GIS has been being researched at home and abroad in order to guarantee the safe operation of GIS. At the same time, PD pattern recognition is still an advanced problem to be studied, and it is difficult to correctly obtain the PD signal from the intense electromagnetic interferences. So this disquisition designs an outer ultra high frequency (UHF) sensor and a pre-positive filter amplifier utilized to monitor the PD signal in GIS, and a plenty of PD data are sampled with artificial physical models of PD defect in laboratory. Meanwhile, this paper introduces how to construct the complex wavelet applied to suppress the interferences, of which the characteristics of simple and multiplex information are introduced. The simulation results and practical application prove the complex wavelet transformation can excellently suppress the white noise and narrow band interference. Finally, associated method of software and hardware is adapted to extract PD signals. The main conclusions are shown as following:The paper uses Greens function to calculate the transient electric field excited by the PD, and develops the simplified expression of the transient electric field, and shows clearly modes' contribution to the transient electric field and Gauss distributed current can be used to simulate the PD pulse. Three artificial physical models of PD defects establish the foundation for sampling plenty of PD data and developing the research of PD mechanism under multiplex defects.Annexed impedance adopted to optimize dipole antenna (DA) makes DA become ultra broadband antenna, which relative bandwidth ratio reaches 0.73. The designed shield resonance loop antenna (SRLA) holds better standing wave ratio (SWR), stronger ability to suppress interferences. On the other hand, the designed microstrip line filter amplifier JBF-1000, which bandwidth is from 300MHz to 1000MHz and the gain is 20 dB, and can effectively improve the signal-to-noise ratio and satisfy the practical application.The phase-frequency characteristic of the complex wavelet has been used to compose the multiplex information of the simple information, and the multiplex information can provide more effective means to monitor the PD signals in GIS and better effect to restrain the noise. This paper introduces the idea and the process of constructing complex wavelet. The complex wavelets based on db wavelet have been expressed according to the way, and the complex wavelet filters are shown based on db3 and db4. Furthermore, the complex wavelet based on db4 is applied to restrain the noise, and the results of the wavelet decomposition and reconstruction suggest that constructed complex wavelet and its algorithms can greatly meet the needs of engineering application.Based on analyzing the main factor influenced the effect of complex wavelet compressing noise, which are threshold selection, decomposition scales, noise level and interference frequency, the paper firstly puts forward the effective wavelet coefficient (EWC) threshold. The results of the simulation and application indicate that the effect of EWC suppressing noise is better than that of maximal theory and Stein unbiased risk estimate theory. Finally, the results show clearly that the multiplex information WTRIPH is the best one, which is composed of real part, imaginary part and phase of complex wavelet transformation.
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