Study On The Topology Detection Of The Grounding Grids Based On Wavelet Edge Detection

As the hinge of power transmission in power systems,electrical substations are of vital importance to the safe operation of the systems.And the grounding grids provide continuous protection for the stable and safe operation of the substations.For many of the known methods which intend to evaluate the corrosion state or diagnose faults of the grounding grids,the detailed configurations including its topology of a particular grounding grid are needed.In order to image the topology of the grounding grids,based on frequency domain electromagnetic method,this paper led an in-depth and meticulous research on: the test status and the interference models of the Directional Peak(DirPk)and Directional Null(DirNull)methods,the upgrading imaging method based on wavelet edge detection,and the optimized detection system and measurement methods.Basic principles of applying the DirPk method and DirNull method were discussed,and tests under substation environment were carried out using two pipeline detectors.To give the error analysis in details,interference models of parallel conductors and intersectional conductors were established respectively,based on the field tests status.And disadvantages of the topology detection using original magnetic signals were demonstrated.A new method for imaging the topology of the grounding grids was proposed based on wavelet edge detection,which had been demonstrated to be of high accuracy and stability.The frame of the method was given comprehensively,which includes the establishment of experiment platform,measurement,preprocessing of the measured data,edge detection,and the parameterization of the topology information.The advantages of the proposed method in its anti-interference ability and high precision were confirmed through simulation and field tests.The effects of magnetic field superposition on locating accuracy are greatly reduced as edge detection can effectively obtain the gradient characteristics of the magnetic field from the noisy background.By ascending the surveying unit to a plane stage,the detecting efficiency is greatly improved compared to DirPk and DirNull.Also,the randomness of the survey path is maintained which ensures the distinguishability of conductors oblique to the survey path and the detectability of conductors around the joints.What's more,due to the strong anti-interference ability of wavelet transform,the noises introduced in the measuring and fitting stage were suppressed to a large extent which ensures the stability of the proposed method in engineering practice.According to the imaging effect under different test schemes,the optimization on the equipment pattern of the detection system and measurement methods were discussed in details.The frequency response of the grounding grid under high frequency harmonic excitation was considered,and a new arrangement way of power lead,which utilizes multiple wires to form a surrounded measurement area approximately,was proposed to reduce the impedance differences between different loops which are formed by the power lead and different conductors.A phase-shift based equipment pattern with multiple power sources and its workflow were introduced.When adopting multiple power sources,it is difficult to arrange the power leads and perform the measurement,thus a new measurement method was suggested to solve this problem.It divides the entire area to several sub-regions and the measuring or edge detection is carried out respectively.Based on a unified coordinate system,the edge detection results in each sub-region are joined together in the end.