A Measurement Of Space Charge In Corona Discharge For DC Transmission Line Based On Acoustic Pulse Method

Controling the corona loss and corona effect at a reasonable level is a key elementfor the development of UHV transmission technology. Study of charge distributioncaused by corona discharge is essential for revealing the microscopic mechanism. Buthow to get accurate space charge distribution for nearly wire has been unresolvedproblem. The acoustic pulse method can theoretically be achieved measuring the spacecharge in real-time, three-dimensional, non-contact, with the advantages which othermethods do not have. Yet in the domestic and overseas, a fully functioned measurementsystem based on this method has not been made.This article taking the lead in researching to the measurement platform, will be ofgreat academic significance and application value. The main contents and results are asfollows:â‘ This article firstly introduced basic principles of the space charge measurementsystem based on acoustic pulse method. The air density changes of the sound effects,the variation of the charge density of the space charge region are studied and discussed.Reasonable simplification and approximation for the actual conditions are introducedand the derivation is: compare to the pressure gradient force, the electric force betweencharged particles can be ignored; the space charge density and air density variate thesame in sound field. Based on this law, spherical coordinates is adopted for deducing theE-field strength of space charges which are modulated by sound wave. The generalexpression of effective signal is verified and the feasibility of this method is affirmated.By the expression the space charge density distribution also can be obtained through themeasured signal.â‘¡Design process and theory basis of the test platform are introduced in deail. Thesignal generator was designed FPGA as control core and achieved the emission of therequired acoustic pulse. The sound insulation room is builded with0.9absorbingcoefficient and80dB noise shielding;According to the simulation data, two sets ofmulti-pin-plate electrode are designed which can generate space charge uniformly withlarge density in a certain area. Refered to lightning electric measuring instrument, achanging E-field measurement antenna is designed. The antenna responds well withinthe scope of voice band and can maintain stable performance under different measuringposition. According to the characteristics of the jamming signal and effective signal, a 2-stage50Hz trap filter is designed which can attenuate power frequency interference70times lower; A1kHz narrow-band-pass amplifier is made with adjustable passbandwidth and magnification.â‘¢Finally,tested the platform by measuring the corona region with known chargedensity distribution. The trend effects of main parameters on the effective signal areanalyzed and the theoretical derivation is preliminary verified. While the platform stillcannot achieve accurate, quantitative measuring, but the validation of basic principlehas shown that through further improve the system can sense the density distribution ofspace charge in3dimension, accurate and real-time.