【作者】 王雪；

【导师】 王晓卫；

【作者基本信息】 西安理工大学 ， 电气工程， 2025， 硕士

【摘要】 近年来,电缆因其重量轻、耐温等级高、输送功率大等优势在城市配电网中得到广泛发展。局部放电(Partial Discharge,PD)检测对于电缆缺陷的诊断与评估至关重要,但现场电磁环境复杂恶劣、存在噪声干扰导致PD信号畸变,影响测试结果的准确性,因此,亟需高效检测方法以准确提取PD特征信息,提高现场PD检测率。此外,电缆深埋于地底,受潮湿环境侵蚀、机械外力破坏、长期过载运行等因素影响,其绝缘缺陷会随时间发展逐渐演变成单相接地故障。及时感知、精准定位有助于加快故障查找速度、保证供电安全和可靠性。然而,电缆型配电网拓扑结构复杂、线路长度短且分支多,故障暂态特征微弱多变。因此,单相接地故障在电缆型配电网的区段定位与精准定位困难。针对电缆这种“潜伏-发展-爆发”的故障演化模式,首先要研究电缆局放信号检测技术,以提高现场PD检测率,加强电缆绝缘缺陷与早期故障的排查;其次,当绝缘彻底击穿形成单相接地故障时,需进行区段定位研究,从而合理部署检修计划;最后,在完成故障区段准确辨识后,需进行精准定位研究,以提升运维效率,缩短停电时间。(1)针对电缆终端与中间接头现场PD检测存在白噪声、周期性窄带干扰,以及局放检测过程中自适应性较弱的问题,首先对电缆局放机理开展研究、计及测试背景噪声,设置高斯白噪声与周期窄带干扰以精准构建PD仿真模型。其次,依据信息熵准确测度图像灰度分布聚集特征,判定PD信号的确定性程度,克服了模态混叠现象,实现对含噪PD信号的准确分解与特征提取;利用峭度对噪声敏感的特性准确区分PD特征信息与噪声干扰分量。最后,将小波分解层数与通用阈值设定相结合,构造了一种与电缆PD相匹配的指数衰减的新型小波阈值函数,提升了现场PD信号检测准确率。(2)针对三相单芯电缆多导体耦合结构复杂,且单相接地故障时的特征微弱、提取不准确,导致电缆型配电网故障区段定位困难的问题,首先提出了一种适合配网三相单芯电缆在两端接地方式下的矩阵变换方法,以频率超过1kHz、误差小于1%的条件基本实现完全解耦,以筛选能够充分反映故障前后暂态特征变化的特征模态,为故障区段的精准定位奠定条件。其次,结合拓扑结构的空间位置合理分布测点,利用矩阵间的信息交互实现逻辑互补。最后,利用电压模态能量与电流模态极性的暂态特征构造判据,实现高精度故障区段定位。(3)针对电缆各相导芯、金属屏蔽层间存在电磁耦合,故障暂态分析复杂且暂态特征提取不准确,导致电缆型配网故障定位精度低的问题,首先研究单芯电缆导体与屏蔽层间的复杂耦合,利用所提解耦方法在一定频率条件下实现完全解耦。其次,从本质上分析解耦后各模态信号的暂态故障特征变化情况与量测可行性,筛选出能够有效反映故障的特征模态构造特征模态阻抗谱。最后,建立频域反射信号到时域脉冲响应的非线性映射关系,将复频域反射系数转换为时域冲激响应,再结合推导计算的修正波速,实现时域信号到空间位置的精确转换,显著提高故障定位精度。更多还原

【Abstract】 In recent years,cable has been widely developed in urban distribution networks because of its lightweight advantages,high temperature resistance,and ample transmission power.Partial discharge(PD)detection is essential for diagnosing and evaluating cable defects.Still,the complex and harsh electromagnetic environment and noise interference lead to PD signal distortion,affecting the accuracy of the test results.Therefore,it is urgent to use efficient detection methods to accurately extract PD characteristic information and improve the detection rate of PD on-site.In addition,the cable is deeply buried in the ground,and its insulation defect will gradually evolve into a single-phase grounding fault with time due to the influence of wet environment erosion,mechanical external force damage,long-term overload operation,and other factors.Timely perception and accurate positioning are helpful to speed up fault detection and ensure the safety and reliability of the power supply.However,the topology of the cable distribution network is complex,the line length is short,and there are many branches,and the fault transient characteristics are weak and changeable.Therefore,it is challenging to locate and accurately locate a single-phase grounding fault in a section of a cable-type distribution network.Aiming at the cable fault evolution mode of "latency development explosion",it is necessary to carry out research on cable partial discharge signal detection technology,improve the PD detection rate on site,and strengthen the troubleshooting of cable insulation defects and early faults;Secondly,when the insulation is completely broken down to form a single-phase grounding fault,it is necessary to carry out section positioning research,to deploy the maintenance plan reasonably;Finally,after the accurate identification of the fault section,it is essential to carry out precise positioning research to improve the operation and maintenance efficiency and shorten the outage time.(1)Aiming at the problems of white noise,periodic narrowband interference and weak adaptability in the field PD detection of cable terminals and intermediate joints,firstly,the mechanism of cable partial discharge is studied,the background noise is taken into account,and the Gaussian white noise and periodic narrowband interference are set to build the PD simulation model accurately.Secondly,according to the information entropy,the aggregation characteristics of image gray distribution are accurately measured to determine the degree of certainty of PD signal,which overcomes the phenomenon of modal aliasing,and realizes the accurate decomposition and feature extraction of noisy PD signal;Using kurtosis sensitive to noise,PD feature information and noise interference components can be accurately distinguished.Finally,by combining the number of wavelet decomposition levels with the general threshold setting,a new wavelet threshold function with exponential attenuation is constructed,which matches the cable PD and improves PD signal detection accuracy.(2)Aiming at the problem that the multi-conductor coupling structure of three-phase single core cable is complex,and the feature of single-phase grounding fault is weak and inaccurate,which leads to the difficulty of cable type distribution network,a matrix transformation method suitable for three-phase single core cable with two ends grounded is proposed,which realizes complete decoupling under the condition of frequency more than 1kHz and error less than 1%,to screen the characteristic modes that can reflect the change of transient characteristics before and after the fault,and lay the foundation for the accurate location of the fault section.Secondly,the measuring points are distributed according to the spatial position of the topological structure,and logical complementarity is realized through the information interaction between matrices.Finally,the criterion is constructed using the transient characteristics of voltage-mode energy and current-mode polarity to achieve a high-precision fault location.(3)Aiming at the low accuracy of fault location in cable-type distribution networks caused by electromagnetic coupling between the conductor and metal shielding,it studies the complex interactions within single-core cables and proposes a decoupling method effective at a specific frequency.The analysis includes changes in transient fault characteristics and the selection of characteristic modes that effectively reflect faults to construct an impedance spectrum.Finally,it establishes a nonlinear mapping between frequency domain signals and time domain responses,facilitating accurate conversion from time domain signals to spatial positions,thereby significantly improving fault location accuracy.更多还原