| With the continuous improvement of the Chinese economic development level and the continuous development of the power industry,power cable as a tool for the transmission of electric energy is more and more widely used in power systems and plays an increasingly important role.When the cable is in normal operation,only a 50Hz power frequency signal exists on the line.When the cable is disturbed or fails,there will be rich high-frequency signals on the line.If the operating status of the cable can be evaluated based on the high-frequency signals,it is of great significance for early warning of the hidden trouble of the cable and improving the stable operation ability of the power system.This paper mainly focuses on the high frequency signal that appear more frequently,including short-circuit fault signal,circuit breaker closing signal,lightning strike signal,and partial discharge(PD)signal.And different types of high frequency signal are analyzed.There is an attenuation of high frequency signal in the process of cable.Based on the transmission theory of high frequency signal in the transmission line and according to the structural parameters of 10kV cable,this paper establishes the cable frequency variation simulation model which considered the effect of the semiconductive layer in ATP-EMTP to study the transmission characteristics of high frequency signal in the cable.The simulation studies the transmission attenuation law of a single frequency signal in the cable,and the research results show that:when the signal frequency is below 1MHz,the amplitude shows a linear attenuation relationship with the propagation distance,and the attenuation is weak.When the signal frequency is 1MHz and above,the amplitude shows an exponential decay with the propagation distance;with the same distance,the higher the signal frequency,the more significant the attenuation effect;and after calculation,the attenuation coefficient of the line is positively correlated with the signal frequency.Then the propagation characteristics of the PD and the lightning signal are simulated,and the results show that the influence of the PD by the propagation characteristics of the cable is far greater than the effect of the lightning signal by the propagation characteristics.Aiming at the problem of high frequency signal identification,this paper builds a 10kV cable power supply system based on the cable frequency varying model.The high frequency signal of a short circuit fault,circuit breaker closing,lightning strike with and without fault,and PD are simulated and analyzed.The time-domain features of various high frequency signal are obtained.The energy distribution features of high frequency signal in different frequency bands are obtained based on wavelet energy analysis.A high frequency signal features recognition algorithm is proposed,which combines the time-domain and wavelet energy distribution features,and a feature identification criterion is constructed.The multi-classification problem is transformed into a two classification problem,and the feature judgment is carried out to realize the classification of multiple high frequency signal.A large number of simulations verify the effectiveness of the proposed feature recognition algorithm.Finally,the health status evaluation of cable is studied.Firstly,the paper studies the calibration method of PD and PD energy of cable according to the attenuation and dispersion characteristics of PD in cable lines.And compares the amplitude calibration method and area calibration method of PD.The integral calibration method is used to calculate the PD of cable.A kind of PD energy calibration method which is based on wavelet packet energy is proposed.According to the multiple indicators of the PD signal of the cable,and considering the development trend of cable insulation degradation,the comprehensive evaluation system of multi-index cable health status is constructed.Based on the characteristics of PD signal,the system is constructed by using the fuzzy analysis method. |
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