基于时频域反射法的高温超导电缆故障定位研究

针对我国超导电缆公里级示范工程的运维需求,采用基于伪Wigner-Ville分布的时频域反射法,测量不同温度和不同类型模拟缺陷下超导电缆的时频信号变化,分析不同温度下时频分析在超导电缆故障定位中应用的有效性,并通过改变入射波的中心频率和带宽,研究入射波形形态对故障定位的影响。模型样缆采用国产35kV冷绝缘三相统包高温超导电缆,缺陷模拟相设置了绝缘缺失、对地绝缘电阻逐渐减小、短路3种类型的故障,检测温度设置为室温、液氮和回温3种环境。结果表明:室温环境下,基于伪Wigner-Ville分布的时频域反射法对上述3种故障反射的反应灵敏度依次增加,定位误差小于3%,入射波的中心频率或带宽越高,引起的衰减越大,定位需要的时间补偿就越多;液氮环境下,针对绝缘缺失和短路的叠加故障,当温度下降至77K附近时,故障处归一化时频互相关峰值随温度的小幅度下降而逐渐减小,且波速明显升高;温度回升过程中,该方法的定位准确度不受温度变化和电缆状态的影响,误差仍小于3%。回温过程中随着温度的变化,超导电缆故障处和末端归一化时频互相关峰值大小发生明显的同步变化,该现象可评估现场超导电缆系统中液氮泄漏导致的温度上升问题。

Research on Fault Location of High Temperature Superconducting Cable Based on Time-frequency Domain Reflectometry

The time-frequency domain reflectometry based on pseudo Wigner-Ville distribution was used to detect the time-frequency signal changes of superconducting cable under different temperatures and types of simulated defects. The effectiveness of time-frequency analysis in fault location was analyzed for superconducting cable at different temperatures. The influence of incident waveform shape on fault location was studied by changing the center frequency and bandwidth of incident wave. The domestic 35 kV cold insulated three-phase high temperature superconducting cable was used as the simulation sample cable. Three types of faults were set, i.e., loss of insulation, gradual decrease of insulation resistance to ground and short circuit. The detection temperature was set as room temperature, liquid nitrogen temperature and temperature recovery, respectively. The results show that the response sensitivity of this method to the above three kinds of fault increases in turn at room temperature, corresponding location error less than 3%. The time compensation needed for positioning increases with the increase of the center frequency or bandwidth of the incident wave. The peak value of time-frequency cross-correlation at the fault decreases gradually with the decreases of temperature for the short circuit in liquid nitrogen environment. The wave velocity increases obviously when the temperature drops to about 77 K. During the temperature rising process, the positioning accuracy of this method is not affected by the temperature change or the cable state. The location error is still below 3%. The change of temperature during the rewarming process can cause obvious synchronous change of the peak value at the fault and the end of the superconducting cable. It can be used to evaluate the temperature rise caused by the leakage of liquid nitrogen.