Research Of Method And Technology On The Defect Diagnosis Of Grounding Grids In Substations

The grounding grids of substations are important measure to keep stable operation of power system and safety of operators or power apparatus. Its grounding capability is always paid much attention by correlated departments. The power system accidents caused by corrosion and broken point faults of the grounding grids are often taken place and economical loss is large in China and India. How to diagnosis the faults condition of grounding grids is a very important problem remained to be resolved. Grounding grids are buried in soil, so it is difficult to acquire their information. A practical and effective diagnosis method and technology without opening grids and stopping operation is needed.Supported by the Scientific Funds for Outstanding Young Scientists of China (No.50325723) and the National Natural Science Foundation of China (50577019), the main innovative results are as follows:1. A new diagnosis method of faults of substations'grounding grids is presented. An exciting current of sine wave is injected directly into grounding grids by two lead wires, and then the distributions of the surface magnetic induction intensities are measured. At last, the corrosion conditions or broken points of the mesh conductors will be found by analyzing the distribution characteristics and comparing with the results of the normal simulation computations. The feasibility and correctness of the diagnosis method and technology are tested by simulation calculations.2. The electromagnetic environments in different substations are measured and analyzed. The electromagnetic interference of work frequency and transient magnetic field are measured in different places near the transformer, CT, PT and mother lines in 110kV, 220kV and 500kV substations. The characteristic of complex electromagnetic environment is given in substation.3. The measuring system of electromagnetic induction intensity in complex electromagnetic environment is designed. The measuring availability of electromagnetic induction intensity is carried out by using these technology measures of amplifier, notch-filter and band-pass filter, and so on. The availability of the measuring system is tested by experiments and its immunity ability, distinguish rate and precision satisfy the diagnosis demands.4. A special sine-wave exciting source of different power frequency system for testing the grounding grids functions and diagnosing faults is designed. Based on technologies of linear amplifying and impedance transformation, the problem of impedance matching between the power amplifier and the load of grounding grid is solved in the conditions of wider frequency band and heavier output current. At the same time, the working frequency and output current can be adjusted continuously. Experimental results show that the frequency characteristics and the abilities of driving load and current output can satisfy the design demands. The practical applications show that the design of the source is reasonable and it can be used to check the grounding system function and examine the fault.5. The faults of broken point and corrosion are simulated by experiments in a testing grounding grid. The diagnosis method and technology are tested and applied in a few practical substations. The testing results show that this diagnosis idea is feasible, this diagnosis method is effective and this diagnosis technology is dependable.