Simulations and experiments of the generation apparatus of the DC electric field with the space charge

To make accurate measurements,field mills must be calibrated in a known DC electric field space charge in which the quantities can be control1ed.A simulation model of the generation apparatus of the electric field with a space charge has been built.Based on the combination of the electric field and the transfer of a dilute substances model,the in-fluence of openings in the metal screen was calculated.Simulation results showed that the opening size of the high‐voltage electrode has a great influence on the distribution of the electric field and ion density at the calibration zone.Next,a generation apparatus was designed and developed and ion mobility was researched.The experimental results showed that ion mobility decreased with an increase in electric field strength.However,ion mobility tends to be saturated when the electric field reaches a certain critical value.Two fitting formulas of ion mobility of positive and negative charge are proposed that can be used to predicate ion mobility in a high electric field.

Dispersion characteristics of switching transients from large‐scale experiments in a 1100 kV gas insulated switchgear circuit

The switching operation of gas insulated switchgear(GIS)disconnector will produce multiple random spark discharges between the gas gaps of the disconnector.Each spark discharge can be affected by various random factors,such as trapped charge on the load side,the initial operating phase,gap distance and operating speed of the disconnector,leading to dispersion characteristics.At present,some studies have mentioned this dispersion,but its impact is still unclear due to the lack of experimental data,resulting in a deviation between the simulation results and the measured results.In this study,thousands of switching operations were carried out based on the 1100 kV full‐scale GIS circuit in Wuhan ultra‐high voltage alternating current Test Base.The maximal information coeffi-cient analysis,linear regression fitting and other statistical methods were used to discuss the dispersion characteristics of very fast transient overvoltage(VFTO)and transient enclosure voltage(TEV)from large‐scale experimental data.The results show that the dispersion of VFTO and TEV in amplitude aspects both increase gradually as the breakdown voltage increases,with the maximum difference of five times of TEV amplitude at normalised breakdown voltage.In terms of frequency characteristics,the dispersion of different fre-quency components in TEV is always greater than that of VFTO,especially for the high‐frequency components.Moreover,by comparing the frequency characteristics of TEV at different positions,we notice that the dispersion is almost independent of the spatial po-sition but only determined by the randomness of spark discharges.These discoveries reveal the importance of the dispersion in switching transients and make up for the lack of theoretical understanding of the correlation among them.