Design Of Grounding Grids Diagnosis System Based On Electrical Impedance Tomography Measurement Principle

The grounding system of substations are not only the important measure to keepthe stable and safety operation of power system, and but also the necessary measure tokeep the safety of operators or power equipments. But the conductors of the groundinggrid are buried in soil perennially, the grounding performance turn worse due to thecorrosion of soil. It may threaten the normal operation of the power system eventually.Therefore, a lot of research on the corrosion diagnosis of the grounding grid has beenmade by many researchers of domestic and overseas. And some diagnosis methods havealready been put forward. The methods are mainly divided into two kinds: one is theanalytical methods based on electrical network theory. Another is the analytical methodsbased on the electromagnetic field theory. At present, the study on the diagnosis of thegrounding grids corrosion are still limited in the theoretical analysis. A diagnosis systemwhich can be used in solving the practical engineering problems is urgently needed.In this paper, the measuring method of the EIT (Electrical Impedance Tomography)was used in the corrosion diagnosis of grounding grids. A set of corrosion diagnosissystem in grounding grids has been designed in this paper after more than a year ofresearch and experiments. The main works and innovations are as follows:①The method of the current injection and the loop measurement which areusually used in measurement of EIT has been used in the corrosion diagnosis ofgrounding grids It can make full use of the node of the grounding grids and obtainuseful information as much as possible.②Through the analysis of the existing measurements methods of the conductorimpedance, the method which used four electrode to capture the voltage data of thegrounding grids in the diagnosis has been put forward. This method can eliminate theeffect of contact resistance on the measurement result, so the data of the measurementcan be more accurate.③A set of excitation source system with FM and AM on the basis of the DDStechnology is designed. The system used the DDFS as the core and adopted theimproved Howland circuit structure which can realize the change of voltage to current.Then it can realize the continuous adjustment of the amplitude and frequency of theoutput current. The excitation source whose amplitude and frequency can be adjustedaccording to actual situation is used to excite the measured grounding grids. ④The automation measurement system for corrosion diagnosis of groundinggrids has been designed. The system is a16-channels data acquisition system whichused the ARM controller as the core. Current channels switching and voltagemeasurements are completed automatically by the system, without artificial in changingwire and connection. And then it can improve the test efficiency greatly and eliminatethe measurement error caused by manual operation.⑤The accuracy of the measurement system has been verified and the feasibilityand effectiveness of the theory of the grounding grids corrosion diagnosis have beenproved through the resistors-network simulation experiment and the field test insubstations.