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132 results on '"WANG, Lijun"'

7. Numerical Simulation of Streamer Development Process in N2/H2 Environment at Elevated Temperature

Author

Zhang, Runming, Wang, Lijun, Liu, Jie, Lian, Zhuoxi, and Wang, Zhiwei

Abstract

In this article, a two-dimensional (2-D) axisymmetric fluid model is built to investigate the streamer development characteristics, as well as the distribution time of each reactive components with pure N2, pure H2, and mixed gases of 50% N2 and 50% H2 at lower voltage and elevated temperature. The results indicate that in terms of thermal breakdown, the insulating properties of pure N2 are stronger than that of pure H2. Under the influence of high temperature, the shape of the ionization rate distribution is no longer a slender wave shape but more spread. In addition, a new ionization area will be formed near the rod electrode, and finally, the ionization region near the rod electrode will merge with the ionization wave head with the increase in temperature. For the mixed gas of 50% N2 and 50% H2, it will dissociate into atoms and recombine under the action of high temperature to form molecules containing both nitrogen and hydrogen elements, such as NH3. NH3 is an electronegative gas, which will greatly enhance the thermal breakdown performance of the mixed gas and makes its dielectric strength second only to pure N2. Therefore, it can be speculated that appropriately increasing the proportion of H2 in the mixed gas will improve both the arc extinguishing ability and the postarc thermal breakdown performance, which has been proven by experiments considering that the arc extinguishing ability of H2 is stronger than that of N2.

Published
2023
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14. Simulation of the thermal process of anode in drawn vacuum arc

Author

Shi, Zongqian, Jia, Shenli, Dong, Hong, and Wang, Lijun

Subjects
Finite element method -- Analysis, Thermal analysis, Business, Chemistry, Electronics, Electronics and electrical industries
Abstract

In this paper, a transient 2-D finite-element model was developed to simulate the anode activities of drawn vacuum arc. Some important thermal processes of anode, e.g., the temperature distribution, melt, and evaporation, have been investigated for copper vacuum arc of 27.5 kA (rms) with different separation current. The dimension of eroded region on anode due to melt and evaporation was simulated and compared with other experiments. Index Terms--Anode, simulation, thermal process, vacuum arc.

Published
2007

15. Experimental investigation of vacuum arcs in nonuniform axial magnetic fields

Author

Jia, Shenli, Shi, Zongqian, Wang, Lijun, Wang, Zheng, and Rong, Mingzhe

Subjects
Plasma engineering -- Research, Business, Chemistry, Electronics, Electronics and electrical industries
Abstract

Experiments were conducted in a detachable vacuum chamber with conventional cup-shaped axial magnetic field (AMF) electrodes and three types Of AMF electrodes with different nonuniform AMFs. The radial distributions of the AMF were varied by introducing ferromagnetic material into the cup-shaped AMF electrodes. The vacuum arc column and the distribution of cathode spots were photographed with a high-speed charge coupled device (CCD) camera. Experimental results indicate that a nonuniform AMF with higher axial magnetic flux density at the contact periphery than that at the center (saddle-shaped AMF) can resist arc constriction and increase the cathode and anode utilization ratios more effectively than the ordinary bell-shaped AMF profile. Index Terms--Axial magnetic field, vacuum arc.

Published
2004

40. Numerical Simulation of Thermal Characteristics of Anodes by Pure Metal and CuCr Alloy Material in Vacuum Arc.

Author

Huang, Xiaolong, Wang, Lijun, Jia, Shenli, Qian, Zhonghao, Deng, Jie, and Shi, Zongqian

Subjects
*ANODES, *VACUUM arcs, *ALLOYS, *VACUUM switches, *THERMAL conductivity
Abstract

Anode material seriously influences the characteristics of vacuum arc and further affects the performance of medium-voltage vacuum switches when the interruption current is high. There are many materials used for electrode manufacture, and different materials are selected for different switches. For a pure metal, its performance usually cannot satisfy the actual requirement. To improve switch’s performance, an alloy is usually used as an electrode material. In this paper, thermal processes of six kinds of metal anodes (including pure metal and alloy anodes) are simulated and researched. The physical parameters of the pure metals all come from experiment results directly or are fitted by the experimental data. The physical parameters of the CuCr alloys are derived from Cu and Cr parameters. Two kinds of temperature calculation methods are used, which are called melting and solidification model and equivalent specific heat method, respectively. Simulation results show that W and Mo anodes have the higher temperature than Cu, Cr, CuCr25, and CuCr50 anodes. A pure Cr anode has the largest melting width and highest saturated vapor pressure and evaporation energy. A Cu anode has the biggest melting depth. A W anode has the smallest melting width and depth. Axial temperature gradient is related to the thermal conductivity, and the Cr anode has the largest axial temperature gradient. The thermal characteristics of CuCr25 and CuCr50 anodes are located between the pure Cu and Cr anodes. There are two melting points appearing in the results of CuCr alloys, and between the two melting points, the alloy anodes are in solid–liquid mixture state. [ABSTRACT FROM PUBLISHER]

Published
2015
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