Study On The Fault Diagnosis Of 35kV Substation Grounding Grid

The grounding grid is an important component of a substation.Its working reliability is important to guarantee safe and reliable operation of the power system.But the grounding grid buried underground may be corroded or ruptured by soil electrochemistry.Its electrical performance may be affected and even lead to power system fault and huge economical loss.So it's necessary to study high-accuracy fault diagnosis of grounding grid.So as to judge the fault location and type without dig the ground.Furthermore,it can repair the grounding grid and guarantee the safe and steady operation of the power system.It's an important premise for study grounding grid performance to calculate grounding parameters.The power frequency parameters calculation method based on unequal potential model and the impulse parameters calculation method based on joint of magnetic and circuit theory are used.A model grounding grid is calculated by these calculation methods,and the results have shown that the numerical results are similar with those obtained by CDEGS,which illustrates the accuracy of the calculation results.Furthermore,when the lightning current immitted from the corner of grounding grid,the GPR will be larger than that from the center of the grounding grid.In order to comprehensive the effect of design parameters of substation grounding grids on its performance,the Sobol' method is used to analyze the sensitivity of several design parameters.By sampling the study parameters with Latin hypercube sampling technique,the sensitivity about the ground resistance can be calculated.The results have shown that the concerning parameters' sensitivity can be well analyzed by Sobol' method.The grounding grid's area and soil resistivity have great effect on the ground resistance of grounding grid,so it should be carefully considered when design the grounding grid.Meanwhile,the burial depth and length of vertical earthing electrodes have strong interaction with other parameters,so if their settle values are to be changed,the other parameters should also be alternated so as to satisfy the design request of ground resistance.Furthermore,the soil resistivity has great impacts on all grounding parameters,so it's essential to measure soil resistivity accurately during grounding grid fault diagnosis.The surface potential distribution is one of the parameters which can show entire grounding grid performance directly.The surface potential distribution is calculated and analyzed based on field-circuit coupling.Then two types of model grounding grids are tested,and their change rule of surface potential is concluded by fault setting.The results have shown that the surface potential of grounding conductor node is larger than that of mesh.When the grounding grid has a fault,the surface potential around the fault point may rise.So,by comparing the surface potential distribution attributed by computation method and site test,the fault location of a grounding grid can be judged.The surface magnetic induction of grounding grid is another parameter which can show entire grounding grid performance.The robust least squares method jointed with Tikhonov regularization is presented to solve magnetic field inverse problem.Then this method is applied on the fault diagnosis method of grounding grid based on surface magnetic induction.The test results of a model grounding grid have shown that using the calculation method proposed can obtain accurate surface magnetic induction with less site test workload,and the method can resist gross error,which enhances the accuracy and efficiency of the fault diagnosis method.Furthermore,the magnetic induction of grounding conductor is larger,and the magnetic induction of current injection point is the largest.When the grounding grid has a fault,the surface magnetic induction of the fault conductor may decrease.Further study on the above fault diagnoses of grounding grid shows that these methods have certain shortcomings.It's hard to tell accurately both the fault type and location using these methods.The change rules of surface potential and magnetic induction when grounding grid has typical faults are summarized.A judging rule of grounding grid state is proposed based on grey relational degree theory according to the change rules.The accuracy of the method is illustrated by a real grounding grid fault diagnosis test.The results have shown that the proposed judging rule can be used to diagnose the grounding grid's fault type and location accurately.The study results may provide new idea and important base for grounding grid fault diagnosis,and may provide reference for optimization design and transform of grounding grid.