A Method For Corrosion Diagnosis Of Grounding Grid

Grounding grid is essential to the safety of substation, however, the corrosion caused by earth may result in thinness even break of the grounding down-lead and horizontal equal-voltage conductor. This will lead to fault spread when grounding fault occurs, and will be dangerous to human and facilities. The obtain the corrosion level of grounding grid, two ways were always employed in the past, one was to measure and record the change of grounding resistance to evaluate the corrosion indirectly and the other was to dig widely to see the corrosion directly. These two ways are either inaccurate or aimless, they both need lots of work and affect the running of power system.A new grounding corrosion diagnosis method based on circuit theory and fault diagnosis theory is introduced in this thesis. This method regards grounding grid as a pure resistance network. The corrosion diagnosis functions are built in application of the law and then solved in use of the topology of real grounding grid and measured data of the resistance between down-leads. The result that will be used in the evaluation of the corrosion level is the change of the grounding grid branch conductance.In this thesis, the accuracy and solve of the diagnosis functions, the improvement of the diagnosis accuracy and the reduction of workload are researched. The main conclusions are listed below:(1) Because the diagnostic functions built are uncertain and nonlinear, so this paper adopt the method of numeric iteration integrated the minimum two-multiply to find the answer of the function, and the process of solution needs little time, the diagnostic outcome is accurate.(2) Putting up with the diagnostic method that measure step by step. The primary measured times are closed by the 10 percent of the whole nodes of the grounding network, then account to the result of the primary measure, make a farther measure. This can reduce the workload of measure, thereby avoid the blindness and also can insure the diagnostic precision.(3) Because the resistance between ground leads is only ten mΩ, The dc double bridge and four-port connection can cancel the effect of the measured wire and in the field contact resistance.(4) In the field, the election of measured nods (ground leads) has important effect on the result of diagnosis. So the measured region should include the ground leads of transformer and arrester.The emulation, experiment and field test indicate that this method has some merits: few measured work, high diagnosis accuracy and the rapid diagnosis speed. This method can avoid the blind test and the lack accuracy. So this method has correspondence engineering-utility value.