| Parameters such as amplitude and phase of three-phase(multi-phase) voltage and current can directly reflect the running status and health level of ac power transmission and distribution lines. They are the main references to assess the power quality, to calculate transmission power, to determine the cutting capacity of reactive power compensation. Besides, whether to start the relay protection and fault diagnosis rely on these parameters as well. Detecting the running characteristics of voltage, current on the overhead transmission lines(TLs) in a safe, accurate and convenient way has great importance to ensure the safety, reliability and economic operation of power system.This paper applies electromagnetic field inverse problem theory to the inversion of transmission line voltage and current. Meanwhile, the methods using ac transmission line electromagnetic field back-stepping transmission lines' electric parameters were discussed. The research content of this paper can be roughly divided into the following four parts:Firstly, various calculation methods of power frequency electric field and magnetic field around ac transmission lines are introduced. The advantages and disadvantages of various methods are stated systematically. In addition, the 2D and 3D calculation method of power frequency electric field and magnetic field around transmission line were compared and analyzed. Moreover, this paper expounds the scope of application of these two calculation ways.Secondly, to realize the inversion from electric field in the vicinity of TL to parameters of line voltage, the theoretical derivation and numerical example validation were provided. Charge simulation method is adopted to establish the calculation model of ac TL electric field. Over-determined linear equations were established using the measured power frequency electric field data of measurement points and calculate model. After the least square solution to the over-determined equations was acquired, the corresponding line voltage values can be obtained as well. Error analysis to the proposed inversion method is put forward. The way to reduce reverse error is introduced. In addition, two kinds of electric field measure point arrangement were introduced. The scope of application to the two arrangements was introduced as well.Thirdly, the inversion process from magnetic field around TL to line current were studied. A new detection method for three-phase currents of overhead transmission line is proposed, in which the measured data of power-frequency magnetic field under transmission lines are used to back-calculate the current values in the conductors by inverse and optimization algorithm. Moreover, some specific measurement points are singled out and the constraint conditions between magnetic field components of the specific measurement points and the currents of transmission lines are deduced. It can greatly reduce the computation complexity of the inverse problem solving. Finally, the simulation analyses verify the feasibility and accuracy of the proposed inversion method.Finally, a new type of electric field measurement sensor were installed in the vicinity of a three-phase ac lines. Thus, the electric field data acquired by the sensor can be recorded. The measured electric field data was substitute into the inversion algorithm proposed in chapter3, the feasibility of the method was verified consequently. The research work was summarized. The research conclusions were provided as well. The key problems solved in this paper were indicated as well as the problems should be studied further. Research results of this paper provide new ideas for non-contact measurement of ac TL voltage or current and on-line monitoring. |
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