Optimalization Of Hilbert Fractal Antenna And Adaptive De-noising For Partical Discharge Monitoring Of Transformers

Power transformer is one of the most important equipment in power system, theinternal fault of transformer is usually due to insulation defects. There is a tight linkbetween the insulation defects of transformer and partial discharge (PD). The PDmonitoring can be used to faults diagnosis for power transformer, and it is valuable toprevent accident faults in power transformer and insure the stable performance of powersystem. The PD approach has already become present research focuses in recent years.However, It is still need further studies on sensing technology, anti-interferencetechnique, PD pattern recognition before the PD on-line monitoring system can beapplied in actual projects. Based on summarize and analyze of the research status of PDon-line monitoring for transformers, this thesis made a systematic and thorough studyon the Hilbert fractal antenna optimization, the noise suppression based on adaptiveoptimal wavelet de-nosing and the chaotic oscillator filter etc., The main contents areshown as follows:①Firstly, thorough research on basic principle of fractal antenna and the practicalsituation of power transformer, the design criterion of UHF antenna and theoptimization design method of Hilbert fractal antenna was put forward. The influence ofwidth, conductor thickness, medium thickness, feed position of the four order Hilbertfractal curve to the performance of the Hilbert fractal antenna, such as voltage standingwave ratio(VSWR), gain, directivity have been analyzed. The optimization designmethod for antenna conductor by internal slotted method was put forward. The optionalfour-order Hilbert fractal slotting antenna was designed through the PD experimentsresults, the bandwidth, VSWR were verified to meet the requirement of PD UHFon-line monitoring.②The adaptive chaotic oscillator filter which can remove the communicationinterference in the PD signals was proposed. The basic principles of chaotic oscillatorinterference filter in suppressing PD signal narrow-band was studied. The method basedon the characteristic that the moving state of chaotic oscillators which was determinedbased on the chaotic phase diagram and Lyapunov exponent. Chaos oscillator filter wasput forward to inhibition the narrow-band interference in UHF PD detections. Thede-nosing results of simulation PD high-frequency signals and PD UHF signals showthat the chaotic oscillator filter denoising effect was better than the two order II R-rated filter.③Based on empirical mode decomposition (EMD) decomposition theory andwavelet threshold denoising method, The denoising methods based on EMDdecomposition and adaptive optimal wavelet method was proposed. The method basedon EMD decomposition, then multiple IMF components can obtained, for each IMFcomponent adopt adaptive optimal wavelet denoising, and then the denoising signal canobtained by adding reconstruction. For the adaptive optimal wavelet method, Accordingto the principle of maximum energy for scale coefficients, the optimal wavelet can beselected adaptively in each scale. The de-nosing results of simulation PDhigh-frequency signals and PD UHF signals show that the EMD with adaptive optimalwavelet de-nosing method presented in this thesis is superior to the standard waveletthreshold method.④According to the problems of PD signals recognition in PD UHF monitoring,the fracal dimension extraction method of IMF component of PD UHF signals wasproposed. The method based on the EMD of PD UHF signals, it can be got more IMFs.The fracal dimension and energy of each IMF calculated as as waveform features forPD UHF signals. Then the FPCM, BPNN were used for the artificial defect dischargeanalyzing. The results show that：the method of BPNN haved a better recognition ratethat the FPCM, and the feature of fracal was better that the energy feature.Through the above research work, this paper realizes broadband optimizationfractal antenna for partial discharge monitoring, further reducing the adaptive partialdischarge signal denoising distortion rate, significantly enhance the UHF partialdischarge signal multiscale feature parameter recognition correct rate, it has a strongpractical value and application prospect.