Three differential equations based on different definitions of current density are compared. Formulation I is based on an incomplete equation for total current density （TCD）. Formulations II and {I1 are based on inc...Three differential equations based on different definitions of current density are compared. Formulation I is based on an incomplete equation for total current density （TCD）. Formulations II and {I1 are based on incomplete and complete equations for source current density （SCD）, respectively. Using the weak form of finite element method （FEM）, three formulations were applied in a spiral coil electromagnetic acoustic transducer （EMAT） example to solve magnetic vector potential （MVP）. The input impedances calculated by Formulation III are in excellent agreement with the experimental measurements. Results show that the errors for Formulations I ＆ II vary with coil diameter, coil spacing, lift-off distance and external excitation frequency, for the existence of eddy-current and skin ＆ proximity effects. And the current distribution across the coil conductor also follows the same trend. It is better to choose Formulation I instead of Formulation Ili to solve MVP when the coil diameter is less than twice the skin depth for Formulation I is a low cost and high efficiency calculation method.展开更多
In this paper,the electrical fields along the insulator surface under different scenarios,such as asymmetric pollution on top/bottom surface,and uneven circumferential distribution of surface pollution,have been calcu...In this paper,the electrical fields along the insulator surface under different scenarios,such as asymmetric pollution on top/bottom surface,and uneven circumferential distribution of surface pollution,have been calculated with finite element method for field simulation.Tests on artificial pollution insulators are conducted to study the 50% withstand voltage U50 of artificial pollution suspension insulators under different NSDD(non-soluble deposit density)and asymmetric pollution on the top/bottom surface,and study the change of leakage current with air humidity under different voltage and different ESDD(equivalent salt deposit density).The result shows that asymmetric top/bottom surface pollution has a greater impact on the insulator electrical field distribution,and the leakage current will jump under low air humidity,if had large ESDD,which has practical meanings to the anti-pollution design of the transmission line under different pollution levels across the country.展开更多
针对工程中对高速磁悬浮列车涡流制动系统(Eddy Current Braking System, ECBS)电磁特性研究不够深入的问题,提出电磁模型并建立制动力与列车运行速度、磁极对数、励磁电流、次级板厚度、励磁线圈匝数、铁芯齿槽结构等参数之间的关系.首...针对工程中对高速磁悬浮列车涡流制动系统(Eddy Current Braking System, ECBS)电磁特性研究不够深入的问题,提出电磁模型并建立制动力与列车运行速度、磁极对数、励磁电流、次级板厚度、励磁线圈匝数、铁芯齿槽结构等参数之间的关系.首先,基于等效电流层法将涡流制动系统分为3个求解区域,并且计算各求解区域内的磁场分布表达式.其次,建立感应电流密度分布模型,计算趋肤效应对次级板材料电导率的影响,并对其进行参数修正.再次,引入次级板材料电导率修正系数,利用各求解区域上的边界条件计算次级板与气隙交界面处的磁通密度表达式.最后,根据麦克斯韦应力张量法推导出制动力表达式,根据磁悬浮列车涡流制动系统的参数搭建三维有限元仿真模型.研究结果表明:在对涡流制动力随速度、励磁电流和次级板厚度3种参数变化情况下的曲线分析可知,解析计算和有限元仿真结果之间的平均相对误差在10%以内,验证了数学解析模型的有效性;制动力随列车运行速度增加,先增大后减小,在速度为50 km/h时出现峰值;制动力随励磁电流、励磁线圈匝数等参数增加而增大;制动力随磁极极距、次级板厚度等参数增加,先增大后趋于平稳;制动力随初级槽深增加先保持平稳,当通过临界点后迅速减小.展开更多
基于A,φ-A法和库伦规范,推导了导体区域和非导体区域的有限元方程及自由空间的边界元方程,通过引入交界面条件,实现了将边界元矩阵等效为有限元矩阵求解的有限元-边界元耦合法(finite element and boundary element coupling method,FE...基于A,φ-A法和库伦规范,推导了导体区域和非导体区域的有限元方程及自由空间的边界元方程,通过引入交界面条件,实现了将边界元矩阵等效为有限元矩阵求解的有限元-边界元耦合法(finite element and boundary element coupling method,FE-BECM)。将FE-BECM应用于TEAM-7问题的计算,验证了该方法处理开域涡流问题的有效性。当FE-BECM应用于运动导体涡流场(moving conductor eddy current,MCEC)问题时,用有限元离散源电流区域和运动部件,用边界元离散自由空间并关联相互独立的有限元区域。该方法克服了常规有限元法使用1套网格处理运动问题所遇到的麻烦。使用有限元-边界元耦合法对单级线圈炮问题进行了计算,验证了算法处理运动导体涡流场问题的有效性。展开更多
基金Project(2014BAF12B01)supported by the Key Projects in the National Science&Technology Pillar Program during the Twelfth Five-year Plan Period,ChinaProject(51405520)supported by the National Natural Science Foundation of ChinaProject(2012CB619505)supported by National Basic Research Program of China
文摘Three differential equations based on different definitions of current density are compared. Formulation I is based on an incomplete equation for total current density （TCD）. Formulations II and {I1 are based on incomplete and complete equations for source current density （SCD）, respectively. Using the weak form of finite element method （FEM）, three formulations were applied in a spiral coil electromagnetic acoustic transducer （EMAT） example to solve magnetic vector potential （MVP）. The input impedances calculated by Formulation III are in excellent agreement with the experimental measurements. Results show that the errors for Formulations I ＆ II vary with coil diameter, coil spacing, lift-off distance and external excitation frequency, for the existence of eddy-current and skin ＆ proximity effects. And the current distribution across the coil conductor also follows the same trend. It is better to choose Formulation I instead of Formulation Ili to solve MVP when the coil diameter is less than twice the skin depth for Formulation I is a low cost and high efficiency calculation method.
基金Project Supported by Key Technology Research Programof SGCC(SGSC[2005]115)
文摘In this paper,the electrical fields along the insulator surface under different scenarios,such as asymmetric pollution on top/bottom surface,and uneven circumferential distribution of surface pollution,have been calculated with finite element method for field simulation.Tests on artificial pollution insulators are conducted to study the 50% withstand voltage U50 of artificial pollution suspension insulators under different NSDD(non-soluble deposit density)and asymmetric pollution on the top/bottom surface,and study the change of leakage current with air humidity under different voltage and different ESDD(equivalent salt deposit density).The result shows that asymmetric top/bottom surface pollution has a greater impact on the insulator electrical field distribution,and the leakage current will jump under low air humidity,if had large ESDD,which has practical meanings to the anti-pollution design of the transmission line under different pollution levels across the country.
文摘基于A,φ-A法和库伦规范,推导了导体区域和非导体区域的有限元方程及自由空间的边界元方程,通过引入交界面条件,实现了将边界元矩阵等效为有限元矩阵求解的有限元-边界元耦合法(finite element and boundary element coupling method,FE-BECM)。将FE-BECM应用于TEAM-7问题的计算,验证了该方法处理开域涡流问题的有效性。当FE-BECM应用于运动导体涡流场(moving conductor eddy current,MCEC)问题时,用有限元离散源电流区域和运动部件,用边界元离散自由空间并关联相互独立的有限元区域。该方法克服了常规有限元法使用1套网格处理运动问题所遇到的麻烦。使用有限元-边界元耦合法对单级线圈炮问题进行了计算,验证了算法处理运动导体涡流场问题的有效性。
