Study On The Inversion Method Of Electrical Parameter For AC Overhead Transmission Lines

With the gradual acceleration of urbanization and the rapidly increasing demand for power supply,the scale of power grids in China continues to expand.Accurately and reliably monitoring the operating state of transmission lines,and timely and effectively avoiding the transmission line faults caused by bad weather or human factors performs great significance for safe and stable operation of power grid.Amplitude and phase of operating voltage and current directly reflect the operating state and health level of transmission lines,and play an important role in the fault diagnosis of transmission lines.The conventional method for detecting electrical parameters of transmission lines is to install transformers in a substation at the end of transmission line.However,the commonly-used electromagnetic transformers have potential hazards to cause ferromagnetic resonance.The accuracy of photoelectric transformer needs to be improved,and it is easy to be influenced by vibration and temperature.To solve this bottleneck problem,this paper proposes a new idea to inversely calculate the operating voltage and current of transmission lines based on the spatial electric field and magnetic field measurement data of AC overhead transmission lines,showing the advantages of safety and convenience in non-contact measurement technology.Based on the positive correlation between the power frequency voltage / current of transmission lines and the spatial power frequency electric field / magnetic field generated by transmission lines,some aspects,such as the electric-field and magnetic-field calculation model of overhead AC transmission lines,the ill-posedness of inverse problem and parameter optimization algorithm,are studied.This study aims at improving the accuracy,stability and wide applicability of the inversion method.The main research contents are as follows.(1)The catenary equations of equally-high and unequally-high transmission lines are established.A 3-D mathematical model between the voltage and electric field as well as a 3-D mathematical model between the current and magnetic field of AC overhead transmission lines are constructed.In order to explore the influence factors of the electromagnetic ill-posed inverse problem,the optimal arrangements of electric field and magnetic field measuring points are analyzed,providing the theoretical guidance for the follow-up work of improving the ill-posedness.(2)In order to improve the ill-posedness of inverse problem,the particle swarm optimization with inertia weight is adopted,and the condition number of the observation matrix is set to be the fitness function of the algorithm.The optimal arrangement scheme is determined by the method of optimizing the electric field and magnetic field measuring points,improving the stability of the inverse solutions.(3)The improved algorithm intermingled with the particle swarm algorithm and genetic algorithm is adopted for the inverse calculation.The selection strategy of the adjustable parameters and the constraints of the parameters to be identified are set.The distribution characteristics of the electric field and magnetic field components under transmission lines are analyzed,and the application of the single component and multi-component inversion method are simulated.The improved inverse optimization algorithm is applied to the simulation examples to inversely calculate the voltage and current of AC overhead transmission lines,verifying the robustness and accuracy of the inversion method with different transmission line structure and operating state.(4)According to the requirement of measuring the instantaneous value of electric field components proposed by this inversion method,three-dimensional electric-field sensor of flat plate capacitance is adopted.The experimental system of AC transmission lines is built.Then,the electric-field experimental measurement and inverse calculation of the algorithm are conducted.The experimental results show that the proposed inversion method has high accuracy and stability in monitoring the operating state of transmission lines.Meanwhile,the experimental process embodies the safety,flexibility and convenience of the non-contact measurement in transmission lines.