Research Of Defect Diagnosis For Grounding Grid Based On The Frequency Domain Characteristic Of Grounding System

The substation grounding grid is the most important approach for guaranteeing power system safety. The faults in substation grounding grid will bring great hidden trouble to the safe and stable operation of the power system, when serious it will cause huge economic losses to the society. Monitoring the state of grounding grid is essential for maintaining substation operation. Since the grounding grid is buried under earth, it is very difficult to diagnose grounding grid defects and determine defect position without excavation. Based on the analysis of frequency domain of grounding system, the frequency characteristics of surface potentials of the electric field response parameters are analyzed in detail in a typical substation after the sine pulse and square-ware sources are injected into the grounding grid. The defect diagnosis method of grounding grid based on the frequency domain characteristic of grounding system is put forward, and the equipment of frequency characteristic parameters about grounding grid is developed. The scale model experiments of small dimension and field experiments of complicated structure are also implemented.The frequency domain model of grounding system has been established. Based on the analysis of frequency characteristics of the soil and grounding conductors, the frequency characteristics model of simple grounding grid is established. The complex frequency model is established adopting the least-square method combining taboo algorithm to inverse the soil structure. The models are verified by software simulation using CDEGS and ANSYS. In the meantime, water slide device has been designed to further verify the model.The grounding system frequency response of the magnetic and electric field parameters is analyzed. Since the surface potential with other parameters has the relation of mutual transformation, the surface potential has been chosen to analyze the sine wave and square-wave source frequency characteristics (from30Hz to100kHz). The grounding grid diagnosis method is proposed to sweep frequency. The fundamental principles, diagnostic procedure and the improvement of diagnosis effect of sweep frequency diagnosis of the grounding grid defects are described.On the basis of above works, the characteristic parameter testers of sine-wave and square-wave for grounding grid are designed and developed. Subsequently, the system software is designed. Firstly, detailed water slide device experiment schemes are designed in the laboratory and the testing of fault diagnosis on the simple grounding grid are performed. Subsequently, the test grounding grid is laid regarding the original grounding grid under the high voltage test hall as the mainly grounding grid, and the detailed measurement schemes of defect diagnosis are explained. Through closing and opening surface switches of laid grounding grid the unbroken and fault instances of grounding grid are simulated. From the analysis of various test data, it is concluded that the method based on the frequency domain characteristic of grounding system can diagnose and locate defect in the grounding grid. It provides a new method for the defect diagnosis of grounding grid.