架空配电线路绝缘水平低,极易遭受雷击产生雷电过电压,从而造成供电中断影响广大人民的生产和生活;对于10 k V架空配电线路,由雷击引起线路闪络或故障的主要因素是感应雷过电压,因此,对架空配电线路感应雷过电压的研究具有十分重要的意...架空配电线路绝缘水平低,极易遭受雷击产生雷电过电压,从而造成供电中断影响广大人民的生产和生活;对于10 k V架空配电线路,由雷击引起线路闪络或故障的主要因素是感应雷过电压,因此,对架空配电线路感应雷过电压的研究具有十分重要的意义。为了提高配电线路的安全可靠性并对线路防雷设计提供有价值的参考依据,基于Agrawal场线耦合模型建立了一种计算感应雷过电压峰值的宏模型,并与时域有限元方法进行了对比验证;结合电气几何模型及蒙德卡罗法对华北地区10 k V架空输电线路进行感应雷跳闸率计算。展开更多
The hot workability of 7085 aluminum alloys with different initial microstructures （as-homogenized and as-solution treated） was studied by isothermal compression tests at the deformation temperature ranging from 300...The hot workability of 7085 aluminum alloys with different initial microstructures （as-homogenized and as-solution treated） was studied by isothermal compression tests at the deformation temperature ranging from 300 to 450 ℃ and the strain rate ranging from 0.0001 to 1 s 1. The strain rate sensitivity of the alloy was evaluated and used for establishing the power dissipation maps and instability maps on the basis of the flow stress data. The results show that the efficiency of power dissipation for the as-homogenized alloy is lower than that of the as-solution treated alloy. The deformation parameters of the dynamic recrystallization for the as-homogenized and as-solution treated alloy occur at 400 ℃, 0.01 s i and 450 ℃, 0.001 s-1, respectively. The flow instability region of the as-homogenized alloy is narrower than that of the as-solution treated alloy. These differences of the alloys with two different initial microstructures on the processing maps are mainly related to the dynamic precipitation characteristics.展开更多
Uniaxial compressive experiments of ultrafine-grained Al fabricated by equal channel angular pressing(ECAP) method were performed at wide temperature and strain rate range. The influence of temperature on flow stress,...Uniaxial compressive experiments of ultrafine-grained Al fabricated by equal channel angular pressing(ECAP) method were performed at wide temperature and strain rate range. The influence of temperature on flow stress, strain hardening rate and strain rate sensitivity was investigated experimentally. The results show that both the effect of temperature on flow stress and its strain rate sensitivity of ECAPed Al is much larger than those of the coarse-grained Al. The temperature sensitivity of ultrafine-grained Al is comparatively weaker than that of the coarse-grained Al. Based on the experimental results, the apparent activation volume was estimated at different temperatures and strain rates. The forest dislocation interactions is the dominant thermally activated mechanism for ECAPed Al compressed at quasi-static strain rates, while the viscous drag plays an important role at high strain rates.展开更多
Methods for improving the high current performance of static induction transistor （SIT） are presented.Many important factors,such as ＂trans-conductance per unit channel width＂ θ, ＂gate efficiency＂ η, ＂sensiti...Methods for improving the high current performance of static induction transistor （SIT） are presented.Many important factors,such as ＂trans-conductance per unit channel width＂ θ, ＂gate efficiency＂ η, ＂sensitivity factor＂ D,and ＂intrinsic static gain＂ μ0,that may be used to describe different aspects of the electrical performance of an SIT are first defined.The dependences of electrical parameters on the structure and technological process of an SIT are revealed for the first time.The packaging technologies are so important for the improvement of high power performance of SITs that they must be paid attention.Testing techniques and circuits for measuring frequency and power parameters of SITs are designed and constructed.The influence of packaging processes in technological practice on the electrical performance of SITs is also discussed in depth.展开更多
文摘架空配电线路绝缘水平低,极易遭受雷击产生雷电过电压,从而造成供电中断影响广大人民的生产和生活;对于10 k V架空配电线路,由雷击引起线路闪络或故障的主要因素是感应雷过电压,因此,对架空配电线路感应雷过电压的研究具有十分重要的意义。为了提高配电线路的安全可靠性并对线路防雷设计提供有价值的参考依据,基于Agrawal场线耦合模型建立了一种计算感应雷过电压峰值的宏模型,并与时域有限元方法进行了对比验证;结合电气几何模型及蒙德卡罗法对华北地区10 k V架空输电线路进行感应雷跳闸率计算。
基金Projects(2010CB731701,2012CB619502) supported by the National Basic Research Program of ChinaProject(CX2012B043) supported by Hunan Provincial Innovation Foundation for Postgraduate,ChinaProject(51021063) supported by Creative Research Group of National Natural Science Foundation of China
文摘The hot workability of 7085 aluminum alloys with different initial microstructures （as-homogenized and as-solution treated） was studied by isothermal compression tests at the deformation temperature ranging from 300 to 450 ℃ and the strain rate ranging from 0.0001 to 1 s 1. The strain rate sensitivity of the alloy was evaluated and used for establishing the power dissipation maps and instability maps on the basis of the flow stress data. The results show that the efficiency of power dissipation for the as-homogenized alloy is lower than that of the as-solution treated alloy. The deformation parameters of the dynamic recrystallization for the as-homogenized and as-solution treated alloy occur at 400 ℃, 0.01 s i and 450 ℃, 0.001 s-1, respectively. The flow instability region of the as-homogenized alloy is narrower than that of the as-solution treated alloy. These differences of the alloys with two different initial microstructures on the processing maps are mainly related to the dynamic precipitation characteristics.
基金Projects(11272267,11102168,10932008)supported by the National Natural Science Foundation of ChinaProject(B07050)supported by Northwestern Polytechnical University
文摘Uniaxial compressive experiments of ultrafine-grained Al fabricated by equal channel angular pressing(ECAP) method were performed at wide temperature and strain rate range. The influence of temperature on flow stress, strain hardening rate and strain rate sensitivity was investigated experimentally. The results show that both the effect of temperature on flow stress and its strain rate sensitivity of ECAPed Al is much larger than those of the coarse-grained Al. The temperature sensitivity of ultrafine-grained Al is comparatively weaker than that of the coarse-grained Al. Based on the experimental results, the apparent activation volume was estimated at different temperatures and strain rates. The forest dislocation interactions is the dominant thermally activated mechanism for ECAPed Al compressed at quasi-static strain rates, while the viscous drag plays an important role at high strain rates.
文摘Methods for improving the high current performance of static induction transistor （SIT） are presented.Many important factors,such as ＂trans-conductance per unit channel width＂ θ, ＂gate efficiency＂ η, ＂sensitivity factor＂ D,and ＂intrinsic static gain＂ μ0,that may be used to describe different aspects of the electrical performance of an SIT are first defined.The dependences of electrical parameters on the structure and technological process of an SIT are revealed for the first time.The packaging technologies are so important for the improvement of high power performance of SITs that they must be paid attention.Testing techniques and circuits for measuring frequency and power parameters of SITs are designed and constructed.The influence of packaging processes in technological practice on the electrical performance of SITs is also discussed in depth.
