The Fault Diagnosis Of Grounding Grids Using Signal Distance Functions In The Substation

The good grounding in the substation is very important for protecting the safety of the station staff and the stable operation of electrical equipment. The grounding grids in the substation is unity of working grounding, protective grounding, and lightning protection grounding, aim at electrical equipment in high and low voltage and protection and automatic devices in power system. The grounding grids provide a common potential reference for various electrical equipments in a substation, not only playing the role of voltage balance, but also discharging fault current when the system is subjected to lightning or short circuit fault, control the maximum potential of grounding grid, to ensure the safety of personal and equipment.Grounding grid buried deep in the ground, the corrosion thinning and rupture of conductors of the grounding grid caused by the long-term effect of soil, while the system is subjected by lightning or the short circuit fault, may cause accidents, and bring tremendous economic losses. The method of Large area excavation is usually used in troubleshooting of the grounding grid in our country, this method is simple, but the blindness, and affect the normal operation of the substation. So there is an urgent need to find a practical and effective diagnostic method in the power system without digging the grounding grid and affecting the normal operation of the substation, to diagnose the location and state of defect of conductors in the grounding grid, and assess the safety performance of the grounding grid. This paper perform the detailed studies on the fault diagnosis method of conductors of the grounding grid in the substation, the main work is as follows:1. Using the CDEGS grounding analysis software package, Establish the simulation model of grounding grid, pouring the excitation current of different frequency sine wave into grounding network based on the principle of electromagnetic induction, and simulat and analyse the distribution of the surface magnetic induction intensity, to diagnosing the defect state of conductors of grounding grid according to the distribution characteristics;2. Analyse the effect of the surface magnetic induction intensity in the case of soil layered structure, the position of injection current and conductors' structure of grounding grid, and study on the distribution of the surface magnetic induction intensity under the condition of corrosion thinning and breakpoint of conductors;3. Comparing and analysing the distribution of the surface magnetic induction intensity of corrosion and breakpoint of conductors of the grounding grid, based on the signal distance function, writing the program of the fault diagnosis of grounding grid through Matlab, to calculate mutual distance function value of each distribution of the surface magnetic induction intensity, and find out the specific difference of the waveform, to diagnose the fault of the grounding grid.