Wang Lei

Selection of the optimal wavelet bases for wavelet de-noising of partial discharge signal

Based on analyzing the influence of wavelet bases selection on the quality of wavelet de-noising, this paper presents a novel method for selecting the best wavelet bases for signal de-noising in partial discharge signal (PDS) processing. The correlation coefficient as well as the signal-to-noise ratio is used for evaluating the optimal wavelet base at present. These two indexes, statistics of meaning, can not reveal the performance of wavelet de-noising comprehensively. In this paper, the concept of information loss assessing coefficient is proposed on the foundation of some contents of wavelet threshold de-noising for the first time, and it is more suited to further analyzing the quality of partial discharge signal. The method is applied during the numerical simulating signals and corona discharge acquisition. From the results it shows that the de-noising procedure can be further refined in selecting the optimal wavelet bases.

Measurement and analysis of Electromagnetic Fields Radiated by Corona Discharge

Corona discharge is a usual type of electrostatic discharge (ESD). Electromagnetic fields radiated by corona discharge could be harm to microelectronic devices of airplane and weapon systems. In this paper, corona discharge current is studied in theory and its characteristics are developed by the analysis of measurement data. Moreover, experiment simulation system of corona discharge is built for simulating corona discharge of spatial objects. Further, the characteristics of electromagnetic fields radiated by corona discharge are developed by time-frequency technology and wavelet analysis methods.

Method of pulse function fitting based on the corona current measurement data

As an important gas discharge form, corona discharge can generate electromagnetic radiation field which will interfere with the electronic devices and systems. Calculation of electromagnetic radiation field requires quantitative research of corona pulse current and analytical expression. According to the research situation abroad that the corona current was fitted using double-exponential function and Gaussian function, a corona pulse current function is proposed in the paper. It is researched based on the physical processes of corona discharge current excitation. And the fitting parameters and analytic of -60 kV negative corona discharge current are deduced based on the measurement data and compared with the double-exponential fitting result. The result shows that time derivative at zero time of fitting expression corona current pulse function is zero. And the waveform frontier is consistent with the measured waveform, which is better than double-exponential function. The proposed fitting method is suitable for describing the corona discharge pulse current waveform.

Analyzing Signals Radiated from Corona Discharge by Fractal Theory

Studying the signals radiation from corona discharge can provide the important theory basis for on-line monitoring and diagnosis of gas insulated substation (GIS) partial discharge. In this text, the wavelet packet and fractal theory were used to analyze the corona discharge signals. Firstly, the corona discharge signals were decomposed to several frequency bands. The fractal dimension of every band was calculated, and the fractal dimension was used as characteristics of signals radiation from corona discharge. The character peaks of signals radiation from corona discharge were determined by fractal dimension, and the differences of different voltage were found.