基于图像特征的输电线路故障行波存续性判别

Identification of the Existence and Persistence of Faulted Traveling Waves for Transmission Lines Based on Image Features

故障行波波头的持续存在是输电线路行波测距和行波保护等得以实施的关键。实际中存在弱故障,现有行波测距与保护缺乏自动判别故障初始波头是否存在和持续,导致行波装置产生错误结果。针对该问题,该文基于初始浪涌波形图像特征及行波在输电线路往复传播规律,提出一种输电线路故障行波波头存续性的判别方法。首先分析了故障行波波头阶跃性和后续行波的产生规律,进而提出构造与初始波头具有良好紧密型的包围盒,计算包围盒内故障行波和外切线构成面积与整个包围盒面积的饱和度,由饱和度判定初始波头的存在。进而对存在初始行波波头的情况,基于后续波头到达时序、波头幅值、斜率等相对特征,实现后续行波持续性判别。大量仿真和现场实测数据表明,该方法能够可靠判定故障行波的存续性,有效避免波头不存在的情况下行波装置的误动。

Nowadays,there have been a lot of research achievements around traveling wave protection and fault location for transmission lines.All these research achievements are based on the premise that the initial surge exists.However,in some cases there is no initial surge,such as weak faults.It is necessary to identify such cases automatically,so that the traditional traveling wave methods can be blocked,and the customized algorithm can be implemented.However,there is no approach to identifying the existence of fault traveling waves.In order to solve this problem,based on the characteristics of initial surge waveform and the regularity of traveling wave propagation on transmission lines,an approach is proposed to identifying the existence and persistence of traveling wavefront of transmission line faults from the perspective of digital waveform image in the paper.Firstly,the generation,propagation and catadioptric process of fault induced traveling waves in AC transmission lines are analyzed.There is a rapid change of the initial wavefront under the action of the fault excitation source,when the fault occurs on the transmission line.And the interval between the initial surge and the subsequent wavefronts is equal,by eliminating the interference of the refraction waves according to the slope of the wavefront.Secondly,a bounding box with good compactness with the initial rapid change is constructed.The area which is composed by the fault traveling wave and the outer tangent line in the bounding box is computed.The saturation of the bounding box is calculated according to the ratio of the computed area and the entire area of the bounding box.The existence of the initial traveling wavefront is determined by the saturation value.Finally,when there is an initial traveling surge,the initial and subsequent wavefronts are calibrated and normalized.The interval between each wavefront is quantized through the triplet data information containing the deviation of wavefront amplitude,the deviation of arrival timing,and the deviation of slope.The persistence of the subsequent traveling waves is identified according to the calculated triplet deviation.A large number of digital simulations and actual fault data record have shown that the initial fault traveling wavefront does not exist when the saturation of bounding box is greater than 0.1.The corresponding traveling wave algorithm can realize blocking and avoid maloperation of traveling wave devices.When the saturation is less than or equal to 0.1 and the subsequent calibrated wavefronts’quantification meets the threshold requirements,the traveling wave fault location methods can correctly determine the fault location.In addition,the proposed method is insensitive to current data or voltage data and can operate correctly.The following conclusions can be drawn:(1)When there is an additional source of fault in the transmission line,the waveform shows a step jump feature.The type of outgoing line at both ends of the fault line remains unchanged during the fault.The fault point persists and the discontinuity of surge impedance has no obvious change.The fault traveling wave shape has repeatability and self-similarity.(2)In a reasonable window where the waveform of the rapid change process can be observed,the fault waveform is approximated linearly and a triangle bounding box closely related to the region of interest is constructed.The saturation of the bounding box can be used to identify the existence of the initial surge.(3)The initial wavefront and the subsequent arrival wavefronts are characterized by the calculated ternary results,and the fault traveling wave persistence can be determined by evaluating the ternary data information of the fault traveling wavefronts.