The Experts below are selected from a list of 318 Experts worldwide ranked by ideXlab platform
Jun Xiong - One of the best experts on this subject based on the ideXlab platform.
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the influence of surface charge accumulation on Flashover voltage of gis gil basin insulator under various voltage stresses
International Journal of Electrical Power & Energy Systems, 2019Co-Authors: Chunjia Gao, Jun XiongAbstract:Abstract Under AC, DC and switching impulse voltages, the surface charges accumulated on the basin insulators of Gas Insulated Substation (GIS) or Gas Insulated Metal Enclosed Transmission Line (GIL) could distort local electric field and even reduce the surface Flashover voltage. In order to quantitatively measure the influence of surface charge accumulation on Flashover voltage of insulator in actual GIS/GIL apparatus, a high-precision 3D surface charge measurement platform and a reasonable model were established for Flashover tests in reference to the insulation design and Flashover properties of actual 220 kV GIS basin insulator. The surface charge accumulation dynamics and corresponding Flashover voltages of the built models under different conditions were captured and analyzed. The results indicate that, as the density of accumulated surface charges increases under either AC, DC or switching impulse voltage application, the surface Flashover voltage would decrease from 62.1 kV to 55.7 kV, namely a margin of 10.3% under AC voltage application. In the context of DC voltage, there appears a 22.8% Flashover voltage drop, from 61.0 kV to 47.1 kV. While for the case of switching impulse voltage, the charge accumulation reduced the Flashover voltage to 52.9 kV with a 13.6% decline from 61.2 kV. Based on the simulation and theoretical calculations, the ‘enhanced electric field zone’ was identified to justify the influencing mechanism of surface charges on Flashover voltage. The research results could contribute to optimal insulation design and fault diagnosis of basin insulator in GIS/GIL.
Masoud Farzaneh - One of the best experts on this subject based on the ideXlab platform.
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Wet Snow Flashover Characteristics of 500-kV AC Insulator Strings with Different Arrangements
MDPI AG, 2019Co-Authors: Fanghui Yin, Zhidong Jia, Qingfeng Wen, Hao Wang, Shunnan Liu, Masoud FarzanehAbstract:In order to study the wet snow Flashover characteristics of 500-kV AC insulator strings under different arrangements, wet snow Flashover tests were carried out in the large climate chamber of China Electric Power Research Institute (CEPRI). The wet snow Flashover voltages were obtained by the even-rising method and the Flashovers were filmed by a camera. The test results showed that the installation of an anti-icing shed of large diameter could increase the wet snow Flashover voltage. The distance between the two insulators was a key parameter that influenced the discharge process and the Flashover voltage. Under Λ-string arrangement, for common insulators, the Flashover performance of iced insulators increased with the connection angle; for anti-icing insulators, the Flashover performance increased at first and then decreased with the connection angle. In wet snow conditions, when the connection angle was at the commonly adopted angle of 60°, the Flashover performance of the common insulators under the V-string and Λ-string arrangements was almost the same. For anti-icing insulators, however, the V-string arrangement was recommended according to the tests. The results obtained in this study can provide a reference for external insulation design in wet snow conditions
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Effects of tower, phase conductors and shield wires on the electrical field around a tower window during live-line work
IEEE Transactions on Dielectrics and Electrical Insulation, 2015Co-Authors: Mona Ghassemi, Masoud FarzanehAbstract:The three-dimensional FEM electric field calculation model of a fiber glass-reinforced plastic (FRP) hot stick during live-line work, which was elaborated in a previous study, could well explain some features of the Flashovers that occurred during a series of cold fog tests at CIGELE. These tests have achieved the most reliable reproduction of four separate FRP hot stick Flashover incidents in Canada at a voltage stress of 105 kV/m at -1.04°C, Relative Humidity (RH) of 109 % with visible fog and 2.8 μg/cm 2 Equivalent Salt Deposit Density (ESDD). However, at the incident site, the geometry is different from that of the laboratory tests. In this paper, a three-dimensional electric field calculation model of a FRP hot stick during live-line work based on the finite element method is proposed to account for the geometry of the Manitoba site incidents at 500-kV. Moreover, the influence of the tower, phase conductors and shield wires on the potential and electric field distribution around an FRP hot stick during live-line work is studied.
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Insulator icing Flashover
2013 Annual Report Conference on Electrical Insulation and Dielectric Phenomena, 2013Co-Authors: Masoud FarzanehAbstract:Atmospheric ice accretion, combined with pollution, has been identified as a significant risk factor in the reliability of line and station insulators in cold climate regions. Flashovers occurring on ice- and snow-covered insulators result from combinations of a number of factors. Electric fields modify the structure of ice, the shape and direction of icicle development, the distribution of liquid water and the geometry of air gaps that break up the continuous ice surface. Electric field strength and voltage polarity as well as corona space charge and ionic wind have demonstrable influences on the Flashover process. Insulator icing Flashover is also affected by changes in air temperature and several other environmental and meteorological conditions including ice type and structure. The presence of surface pollution and the rejection of ions from solid to liquid layers during the freezing and melting process also play a central role in the icing Flashover of insulators, which can occur at normal operating voltage under the most adverse conditions. This lecture presents an overview of these phenomena and describes the interactions that lead to the initiation and development of discharges on the ice surfaces covering the insulators, as well as their evolution to Flashover. The lecture also includes the modeling of these phenomena, leading to successful prediction of withstand voltage as well as to insight into the most practical solutions for improved insulator design and mitigating icing Flashovers.
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The influence of applied voltage on the surface conductivity of atmospheric ice deposited on insulating surfaces
Conference Record of the 1996 IEEE International Symposium on Electrical Insulation, 1996Co-Authors: Masoud Farzaneh, X. Chen, J ZhangAbstract:In the present paper, the effect of applied voltage on the conductivity of both the inner and outer surfaces of atmospheric ice accreted on an insulating surface was investigated. The results were compared with those obtained on a polluted insulating surface. During the development of the flashhover arc, an equivalent surface conductivity for an insulating surface covered with ice was defined. A linear relationship between the equivalent surface conductivity of ice and the conductivity of freezing water was established. The results obtained are helpful for characterizing and modeling Flashover arcs on actual HV insulators covered with ice.
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Flashover Performance of Insulators In the Presence of Short Icicles
International Journal of Offshore and Polar Engineering, 1993Co-Authors: Masoud Farzaneh, O.t. MeloAbstract:This work chiefly presents the results or'a laboratory investigation of ac leakage current and ac Flashover on a short insulator string. The string was partially iced with supercooled droplets at _1.5°C simulating a rime fog, this being one of the factors responsible for a large number of Flashovers on Ontario Hydro's 500 kV system in March 1986. It was found that the leakage current of insulators in the presence of short icicles was very small and consequently no Flashover occurred under normalline-to-ground voltage applied to the insulators. Flashover was produced only under an applied voltage about 80% higher than normal voltage. It was concluded that the presence of fog was associated with the Flashovers occurring in March '86, but that other parameters such as insulator surface contamination and water condensation were also active factors contributing to these Flashovers.
Karl Borg - One of the best experts on this subject based on the ideXlab platform.
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Effects of electrode size and solid barrier orientation on streamer discharge in transformer oil
Journal of Applied Physics, 2014Co-Authors: J. Jadidian, Markus Zahn, Nils Lavesson, Ola Widlund, Karl BorgAbstract:Geometrical effects of electrodes and solid barriers immersed in transformer oil are investigated on positive streamer initiation, propagation, and transformation to surface Flashover using a 2-D axisymmetric model. Electrode radii of curvature in the range of 20 μm to 6.35 mm are selected such that only positive streamers form. Modeling results indicate that the positive electrode size directly determines the streamer initiation voltage, while breakdown voltage and delay are mainly determined by the grounded electrode size. Specifically, sharper positive electrodes require lower voltages to initiate positive streamers and sharper grounded electrodes result in lower delays and higher breakdown voltages. Incorporating perpendicular and parallel orientations of solid barrier interfaces in the electrohydrodynamic model shows that polarization forces from the barrier dielectrics on charge carrying streamers are proportional to the permittivity difference between transformer oil and the solid dielectric. If the barrier permittivity is greater than the oil permittivity, the solid dielectric applies an attractive force on the volume charge that turns the streamer into a surface Flashover expanding on the barrier surface. On the other hand, a low permittivity pressboard interface repels the approaching streamer. Theoretical analysis of electric field propagation and charge distribution along the streamers, surface Flashovers, and through the interfacial surfaces is presented. Barrier dielectric relative permittivities of 1.1 and 4.4 have been studied while the oil relative permittivity is assumed 2.2.
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surface Flashover breakdown mechanisms on liquid immersed dielectrics
Applied Physics Letters, 2012Co-Authors: J. Jadidian, Markus Zahn, Nils Lavesson, Ola Widlund, Karl BorgAbstract:Flashover formation and expansion mechanisms on the surfaces of different dielectrics immersed in transformer oil have been numerically analyzed. Streamers emanating from a needle electrode tend to transform to surface Flashovers if the immersed dielectric permittivity is higher than the liquid permittivity and/or the dielectric interfacial surface cuts the path of the streamer. Perpendicular interface of the immersed dielectric impedes the breakdown by deflecting the streamer and slowing down the surface Flashover. The parallel dielectric interface, however, assists the breakdown by regulating the surface Flashover velocity to an approximately constant value (∼10 km/s).
Chunjia Gao - One of the best experts on this subject based on the ideXlab platform.
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the influence of surface charge accumulation on Flashover voltage of gis gil basin insulator under various voltage stresses
International Journal of Electrical Power & Energy Systems, 2019Co-Authors: Chunjia Gao, Jun XiongAbstract:Abstract Under AC, DC and switching impulse voltages, the surface charges accumulated on the basin insulators of Gas Insulated Substation (GIS) or Gas Insulated Metal Enclosed Transmission Line (GIL) could distort local electric field and even reduce the surface Flashover voltage. In order to quantitatively measure the influence of surface charge accumulation on Flashover voltage of insulator in actual GIS/GIL apparatus, a high-precision 3D surface charge measurement platform and a reasonable model were established for Flashover tests in reference to the insulation design and Flashover properties of actual 220 kV GIS basin insulator. The surface charge accumulation dynamics and corresponding Flashover voltages of the built models under different conditions were captured and analyzed. The results indicate that, as the density of accumulated surface charges increases under either AC, DC or switching impulse voltage application, the surface Flashover voltage would decrease from 62.1 kV to 55.7 kV, namely a margin of 10.3% under AC voltage application. In the context of DC voltage, there appears a 22.8% Flashover voltage drop, from 61.0 kV to 47.1 kV. While for the case of switching impulse voltage, the charge accumulation reduced the Flashover voltage to 52.9 kV with a 13.6% decline from 61.2 kV. Based on the simulation and theoretical calculations, the ‘enhanced electric field zone’ was identified to justify the influencing mechanism of surface charges on Flashover voltage. The research results could contribute to optimal insulation design and fault diagnosis of basin insulator in GIS/GIL.
Yonghong Cheng - One of the best experts on this subject based on the ideXlab platform.
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Influence of pulse front steepness on vacuum Flashover characteristics
Applied Surface Science, 2018Co-Authors: Jiale Mao, Shuang Wang, Yonghong ChengAbstract:Abstract Studying Flashover characteristics in vacuum environment is extremely significant for designing reliable insulation structures. The waveform of applied voltage excitations greatly affects the Flashover process. In this study, the influence of nanosecond pulse front steepness on Flashover process in vacuum is investigated. Firstly, Flashover experiments with nanosecond pulses are conducted. Nanosecond pulses with different front steepness are generated and used to trigger Flashovers on sample surface. The relationship between pulse front steepness and Flashover voltage is studied. Meanwhile, a particle-in-cell with Monte Carlo collision (PIC-MCC) two-dimensional self-sustaining discharge model based on secondary electron emission avalanche (SEEA) scheme is established. The distribution of charged particles, electric field and their evolution during Flashover process are presented. Furthermore, pulses with various rising steepness are applied to the model. The multiplication and propagation of charged particles in different pulse waveform conditions are studied. In all conditions, two stages during Flashover process can be obviously distinguished based on charged particle number evolution which divides the overall Flashover delay time into two parts. By analyzing the voltage development in these two time slots, the quasi-linear relationship between pulse front steepness and Flashover voltage in nanosecond pulse Flashover in vacuum is explained.