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| 1 | Surface charge accumulation and preflashover characteristics induced by metal particles on the insulator surfaces of 1100 kV GILs under AC voltage显示文摘With the increase in the voltage and capacitance of gas-insulated transmission lines(GILs),the insulation failure of GIL has attracted more and more attention.Further understanding of the partial discharge(PD)and flashover characteristics of metal particles on the insulator surface,as well as the flashover mechanism,is necessary to reduce the failure rate and improve the reliability of the equipment.In this study,an ultra-high voltage(UHV)AC insulator PD test and measurement system based on the cross-reference pulse current(PC)and ultra-high frequency(UHF)methods were established.The PD development and flashover characteristics of 5 mm-long metal particles at different positions on the surface of a UHV AC insulator,as well as the surface charge accumulation,were studied.The results show that the discharge of millimetre-scale metal particles on the insulator surface under PD test conditions is relatively low(generally lower than 2PC),and it is difficult to be detected by the conventional PC and UHF methods due to their insufficient sensitivity.Moreover,it is found that the weak PDs of the millimetrescale metal particles will result in a charge accumulation on the insulator surface under AC voltage,which eventually will lead to the insulator flashover.The PDs of the UHV AC insulator before flashover are generally small,which will make it difficult for online monitoring systems to give an effective alarm before flashover. | Li Xing Liu Weidong Xu Yuan Chen Weijiang Bi Jiangang | 2020 | High Voltage2020，5，2： | 4 |
| 2 | Review of the decomposition characteristics of eco-friendly insulation gas显示文摘As one of the major concerns of climate change,identifying a proper eco‐friendly insulation gas for replacing sulphur hexafluoride(SF_(6))becomes a prominent research topic in recent years.c-C_(4)F_(8),CF_(3)I,C_(5)F_(10O),C_(6)F_(12O)and C4F7N are some potential al-ternatives that are proved to have excellent characteristics,including high insulation strengths and low Global Warming Potentials(GWPs).Beyond these key factors,the decomposition products of these alternatives are closely related to the gases'insulation performance,as well as the safety of operators and the compatibility with other materials.In addition,the type and content of decomposition products can be used for fault diagnosis.Therefore,a number of studies were carried out to reveal the decomposition mechanism of these alternative gases,and then to explore the gases'application feasibility and strategy.The recent advances obtained in these studies,including theoretical calcu-lation methods,detection of gas decomposition products,decomposition mechanism are reviewed,and some perspectives for future works are proposed.It is concluded that the phenomenon of solid matter precipitation in c-C_(4)F_(8)and CF_(3)I gas decomposition cannot be ignored and that more research is needed to reveal the influence of buffer gases,micro‐aerobic,micro‐water and other impurities on the gas decomposition process. | Yuan Yang Keli Gao Lijian Ding Jiangang Bi Shuai Yuan Xianglian Yan | 2021 | High Voltage2021，6，5： | 3 |
| 3 | Proposed methodology for online frequency response analysis based on magnetic coupling to detect winding deformations in transformers显示文摘Frequency response analysis is widely used as a method for the offline diagnosis of winding deformations in power transformers.To apply it to a working transformer,people need to determine how to inject the excitation signal and measure the response signal for windings that bear a rated voltage and current.In this study,a method to obtain the frequency response curve online is proposed.It uses the principle of magnetic field coupling to inject a frequency sweep signal into the windings through a Rogowski coil.Another Rogowski coil sensor placed at the root of a high-voltage bushing is used to measure the response current signal.Experiments on a 72.5 kV bushing show that metal accessories of the bushing have no influence on the injection or the measurement.The feasibility of this method was verified by experiments on charged 110/35/10 kV transformers at a factory and a working 35 kV transformer in a power station.The results show that it is safe to install the Rogowski coil at the root of the high-voltage bushing.The excitation signal can be injected into live windings and the response signal is measurable.Strong electromagnetic power frequency noise can be reduced and the frequency response curve can be measured online. | Yangchun Cheng Jiangang Bi Wenzhi Chang Yuan Xu Xiaohua Pan Xianwei Ma Shuai Chang | 2020 | High Voltage2020，5，3： | 2 |
| 4 | Influence of micro-water on AC breakdown characteristics of C_(4)F_(7)N/CO_(2)gas mixture under non-uniform electric field显示文摘The application of eco-friendly C_(4)F_(7)N/CO_(2)gas mixture has become a hot topic in the power industry.To obtain the influence law of micro-water on the AC insulation characteristics of C_(4)F_(7)N/CO_(2)gas mixture,breakdown tests were carried out under different non-uniform electric fields and micro-water volume fractions.With the gap distance of 1 mm and the electric field non-uniform coefficient less than 4.42,the breakdown voltage is positively correlated with gas pressure.With the gap distance of 6 mm and the electric field non-uniform coefficient of 9.28,the breakdown voltage shows a typical N-type change trend with the increase of gas pressure.With the gap distance of 9 mm and the electric field non-uniform coefficient up to 16.45,the breakdown voltage shows a typical N-type change trend with the increase of gas pressure.Micro-water has a negative effect on breakdown voltage under different electric fields,meanwhile the breakdown voltage of slightly non-uniform electric field is greatly affected by micro-water,and the influence of micro-water on breakdown voltage is different under different gas pressures.Therefore,the influence of operating gas pressure and slightly non-uniform electric field should be considered when the micro-water control index of C_(4)F_(7)N/CO_(2)gas mixture insulated equipment is formulated. | Yuan Yang Keli Gao Jiangang Bi Lijian Ding Shuai Yuan Guangzhen Wang | 2022 | High Voltage2022，7，6： | 0 |
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