| With the development of the power system, The scale of power cable lines becomes larger. Among them, the cross-linked polyethylene(XLPE) cable is the most frequently used at present, it is one of the most widely used. XLPE cable is an important tool for the transmission of electrical energy and its reliability can directly affect the safety and stable operation of the power system. So it is particularly critical to monitor the XLPE cable insulation aging condition and locate the PD source in the distances.When PD pulse signal transmitted along the cable, which not only would happen their own severe attenuation distortion, but also would be disturbed by the surrounding signal. Research has shown that PD signal is a kind of chaotic nature of the signal in the cable. And the chaotic signal has a strong anti-jamming capability, so that it makes PD chaotic time series characteristic parameter less susceptible to electromagnetic interference. This paper is on the basis of research that the mechanism of partial discharge and the diagnosis of the cable insulation aging, based on chaotic time series analysis method, the XLPE cable insulation aging diagnostic and PD positioning methods were studied further. Thesis main work:(1) Thesis research the calculation method of partial discharge signals chaotic characteristic parameters. Three kinds of time delay and embedding dimension calculation methods were comparative analyzed and Matlab simulation calculated, we found that C-C algorithm is more suitable for the collection to the PD signal time delay and embedding dimension calculations.(2) Wavelet de-noising approach was used to de-noise the noise signal of actual PD signal and the before and after de-noising PD chaotic signal characteristic parameters were comparative analyzed. We found that chaos characteristics of before and after de-noising PD parameters have obvious change. The calculation results show that: noise signal has great influence to calculate chaotic characteristic parameters, in order to get an accurate amount of real chaos characteristic of PD signal, it is very necessary to.use wavelet de-noising for the initial noisy PD signal.(3) Considering the impacts of skin effect and semi-conductive layer and other factors, MATLAB/Simulink toolboxes are used in the paper to build the simulation model of XLPE cable partial discharge transmission. The decay law of partial discharge signal that transmit along XLPE cable has studied in this paper, with the transmission distance increasing, the waveform of PD signal gradually distortion and broadening, high-frequency components decay seriously. It prove that XLPE cable has the same characteristics with a low-pass filter. By studying the law of PD chaos characteristic parameters that transmitting along XLPE cables through simulation, it found that with transmission distance increasing, the maximum Lyapunov exponent λ will gradually stabilize. Therefore, the maximum Lyapunov exponent λ is used in this paper as the characteristic value to reflect the XLPE power cable insulation aging. With the transmission distance increasing, the trend of correlation dimension is decreasing according to the logarithmic function, based on this special function relationship of correlation dimension, we propose a new method of local location based on chaotic characteristics. The new method has been validated through simulation data and indicate that the new local location method is an effective and feasible method. |
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