Research On Corrosion Diagnosis Of Substation Grounding Grid And Its Influence Factors

The security and reliability of power system is affected by the safe operation of substation, and the complete and reliability of grounding grid is the security of substation. The conductors which constitute the grounding grid are buried under ground, the situation that makes poor electrical connection in conductors is caused by bad weld and the effect of electric power of earth short-circuit current, especially severe soil corrosion by several years. Corrosion of grounding conductors and broken grounding grids will cause disqualification of grounding resistance, step voltage, and touch voltage in substations. So, testing the break point and corrosion situation in grounding grid, identifying and excluding the hidden fault, and preventing the harm from poor grounding is particularly important.Currently, experts have proposed some principle and mathematical model about fault diagnosis of grounding grid, but lacking of engineering practicability. This thesis presents a comprehensive optimization diagnosis method that applies circuit theory, together with some principles for selecting the most sensitive and effective ports for conducting minimum measurements to detect the suspect faults. This method has proved to be engineering practicability by field experiment in substations. But in order to improve the accuracy of diagnosis result, some influence factors existing only in filed test should be taken in account, such as inaccurate grounding grid drawings, offsetting of grounding down lines, and some interference.This thesis mainly studies content for theory and method of erosion diagnosis of grounding grid.1 For steel frame in substation is also connected with grounding grid, and forming a resistance branch of grounding grid. Assuming frame conductor connected at edge and internal of grounding grid, a total of 8 cases, simulating and computing the diagnosis results compared with ignoring the influence of frame conductor. Meanwhile, conventional frame resistance in 110kV, 220kV, 500kV substation is calculated. These resistance data will guide the deeper simulation of frame branch influence in grounding grid corrosion diagnosis.2 Focus on the problem of grounding down lines'deviation existing only in field test, the deviation is set to four levels. Through the simulation and experiment, we draw the conclusion that when the deviation increases, the increases multiple of eroded branch resistance reduces, while the quantity of pseudo-fault branch and its increase multiple of resistance increase.3 Taking substation cable channel conductor which also connected with grounding grid and form electrical circuit into grounding grid erosion diagnosis, by simulating and calculating, the diagnosis result will be more accurate if the cable channel conductors add into grounding grid structure.4 Real world field test of corrosion diagnosis of grounding grid is taking at two substations. Results demonstrate that it is a relatively simple, effective and practical approach for grounding grid corrosion diagnosis.