Study On Space Charge Measurement In Negative DC Corona Based On Sound Pulse

The development of UHV power transmission projects is still an important measure for the development of China's power industry.The rapid development of UHV transmission project puts forward more stringent requirements on the assessment method of the electromagnetic environment.Among them,the ion flow field is an important parameter for calculating and evaluating the electromagnetic environment.Although proposed numerical model for the corona discharge calculation of power transmission line has achieved good results in calculation accuracy,computational efficiency and algorithm stability,the understanding of the mechanism of corona discharge is still not thorough,resulting in big differences between calculation results and on-site measurement.This difference is particularly pronounced under complex conditions and extreme weather conditions.Compared to the numerical model,the experimental measurement of the space charge provides a more direct and effective evaluation method.The measurement results of the space charge directly reflect the distribution characteristics of the space charge during corona discharge,and can more effectively guide the evaluation of the engineering electromagnetic environment.Therefore,the research on the experimental measurement of the space charge has a positive guiding significance for the construction of UHV transmission lines.Secondly,by measuring the distribution characteristics of space charge under corona discharge,it is helpful to further study the problems in the theoretical calculation model,and it will also contribute to the further improvement of the theoretical model.In general,the experimental measurement of space charge has important theoretical research and practical application value of engineering.This paper first explores the method of space charge measurement.After a large amount of preliminary experiments,a numerical model of space charge measurement based on the acoustic pulse method was proposed,and a test platform was built to demonstrate the effectiveness of the proposed numerical model for space charge measurement.Aiming at measuring the space charge distribution inside the corona discharge,a numerical model of gas space charge measurement under the corona cage model was established.The model deal with three key parameters of space charge measurement,including gas pressure,charge density and acoustic excitation electric field.In a unified way,the numerical obtain the relationship between the three parameters and the solution method are obtained.This paper also builds a space charge measurement platform for a corona cage structure.Finally,using this measurement platform,the space charge of DC negative corona gas in corona cage is measured for the first time.The experimental results and theoretical results are analyzed in detail,which indicates the direction for the improvement of the theoretical model.The main innovative achievements of the thesis are:(1)Based on the principle of finite difference,a numerical model for space charge measurement is proposed.The numerical relationship of three key parameters(sound pressure,charge density and acoustically excited electric field)in the space charge measurement are studied;In addition,space charge measurement are discussed in the evenly distribution,one-dimensional distribution,two-dimensional and three-dimensional distribution problems,their design requirements are also included;finally,a space charge measurement method based on acoustic pulse method was obtained.(2)For the space charge measurement inside the corona cage,a numerical model of space charge measurement was proposed.The distribution characteristics of sound pressure and ion flow field in the corona cage under ultrasonic transducer were obtained.The time characteristics and frequency characteristics of the acoustic excitation electric field generated by the space charge under the action of acoustic pulses are obtained.Furthermore,the numerical relationship between the sound pressure,charge density and the acoustic excitation electric field and the solving algorithm are proposed,and correspondingly,space charge measurement platform was established.(3)Based on the space charge measurement platform and numerical model of space charge measurement,the measurement of the space charge under DC negative corona in the corona cage is realized for the first time;three representations based on the cos similarity,the Pearson correlation coefficient and the maximum charge density ratio are achieved for in-depth discussion between measurement results and theoretical calculation results,which points out the problems in the theoretical model and the application of space charge measurement.