Study On Sub-cycle Disturbance Detection Method For Cable Initial Fault

Power cable is an important primary component of power system,whose safe operation directly affects the reliability of power supply system.Local defects of power insulation are often easy to develop into permanent failure,resulting in unplanned power outage.The research shows that when the local defects develop to a certain extent,the sub-cycle disturbance is easy to be observed in the cable voltage waveform.If the disturbance can be detected and extracted,it will be beneficial to replace the defective cable before the permanent failure of the cable and prevent the short-circuit fault.The detection of sub-cycle disturbance needs to be carried out online.Therefore,this paper studies the online detection method of sub-cycle disturbance signal caused by local cable defects,proposes two algorithms that can quickly identify the sub-cycle signal,and verifies them through simulation.The main research contents are as follows:(1)Waveform characteristics of sub-cycle disturbance signals obtained from experiments were analyzed.Waveform similarity method and Bray-Curtis similarity scoring function were used to compare the similarity between waveforms containing disturbance and the reference waveforms to identify the waveforms containing sub-cycle disturbance.The method can correctly identify the sub-cycle disturbance signals generated by simulation and experiment,and can also eliminate the non-sub-cycle disturbance.(2)According to the characteristics of small amplitude variation and short duration of sub-cycle disturbance,a sub-cycle disturbance analysis method based on amplitude ratio is proposed.Based on the tracking function of Kalman filter,the fundamental amplitude of the simulated signal and the measured signal is estimated.The characteristic of the estimated signal waveform is that there is obvious anomaly only when the disturbance occurs,and the estimated amplitude and the disturbance amplitude have obvious correlation.Then,Parzen window function is used to estimate the probability density of the obtained fundamental amplitude,and sub-cycle disturbance discrimination is carried out by comparing the proportion of normal amplitude and perturbation amplitude area in the probability density curve.(3)In view of the characteristic that the disturbance signal detected by the detection device is the attenuation signal after transmission through the cable,the cable is modeled in the PSCAD software,and the measured sub-cycle disturbance is injected into the cable to analyze the attenuation of the sub-cycle disturbance signal in the time domain and frequency domain when it is propagated in the cable.Waveform similarity analysis method and amplitude ratio analysis method are applied to verify the detection effect of disturbance signals after cable propagation and attenuation,and the validity range of the above methods is obtained.