| The voltage and current in power system can directly reflect the operating state of the power grid,therefore,accurately measuring the voltage and current has very important significance both for maintenance personnel judging the state of the power grid safety and the stable operation of power grid.At present,the voltage detection in power distribution system is mainly realized by voltage transformer.With the development of our country's 'strong smart grid',it is more and more urgent to detect the voltage of transmission line online.However,the installation of voltage transformer on the transmission lines has encountered manly problems and it is even impossible to be realized.Faced with such a bottleneck problem,it is necessary to develop a new idea for voltage detection.The detection of voltage for transmission and distribution network is mainly by voltage transformer at present.With the further progress of projects,such as China's West East electricity transmission project,the on-line monitoring for transmission lines becomes imperative.Traditional manual line inspection is a waste of human resources because of the disadvantages such as large manpower input,small line of inspection and so on.Although it is convenient and feasible in theory to realize the on-line monitoring of power transmission line voltage by voltage transformers,there are too many difficulties in large-scale use due to the limited conditions of voltage transformers.Therefore,a new method for on-line monitoring of transmission lines is needed.Our research team has verified the forward problem and inverse problem of electromagnetic field for a long time,and verified the feasibility of calculating the line voltage by measuring the electric field under lines,which makes it possible for non-measuring line voltage.To achieve these goals,it is important to measure the electric field according to the needs of inverse problems.So it is necessary to develop a new kind of electric field measuring instrument and design the measuring points.This paper discusses theoretically and experimentally the three-dimensional sensor,needs of measuring electric field in multiple points synchronous,and some influence factors.The main contents are as follows:(1)A three-dimensional hexahedron electric field sensor is designed according to the needs of 3-D electric field measuring.Based on the electromagnetic induction principle and measuring principle,the linear relationship between induced measuring voltage and electric component is derived.The feasibility of measuring electric field by sensor we designed in sinusoidal AC field is proved.(2)Design the hardware circuit and controlling program.Considering the large equivalent impedance of sensor,the signal extraction circuit is designed particularly,as well as the adaptive amplification circuit and voltage clamp circuit.A kind of wireless start-up mode is proposed to realize the synchronization measuring,and the data time difference caused by distance difference of measuring points is evaluated quantitatively.(3)Establish the plate of experiment to simulate the power frequency electric field under transmission lines,and the electric field measuring system is experimented.Firstly,the measuring system is corrected,after that,the discipline how body and trees influence the measuring is studied.To verify the accuracy and synchronism of the measuring system,the experiment is designed under the three phrase transmission lines in a power station.(4)Considering the fact that the conditional number of inverse operator is influenced by the measuring points,as well as the accuracy of solution,the scheme how to arrange the optimal points is analyzed.Based on the inertia weight which can adjust adaptively,modified particle swarm algorithm is proposed.Using the algorithm,the optimal points in the preset area can be calculated,which will make the conditional number minimum,so the ill-posedness of inverse problem is improved. |
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