高压直流(high voltage direct current,HVDC)输电线路两端的平波电抗器和直流滤波器构成现实的边界元件,对暂态电压高频分量呈带阻传变特性,来自直流线路区外的高频电压信号通过平波电抗器和直流滤波器后被衰减,其能量显著减小,不同频...高压直流(high voltage direct current,HVDC)输电线路两端的平波电抗器和直流滤波器构成现实的边界元件,对暂态电压高频分量呈带阻传变特性,来自直流线路区外的高频电压信号通过平波电抗器和直流滤波器后被衰减,其能量显著减小,不同频带的高频电压信号小波能量可应用小波变换求得。利用区内、外故障时于保护安装处获得的暂态电压小波能量的显著差异来构造直流输电线路区内、外故障判据;利用故障暂态电压小波变换模极大值,构造启动判据;利用正极和负极暂态电压分别与+800和-800kV的相关系数,构造雷击干扰识别判据;利用两极线极波,构造故障选极判据。给出了特高压直流(ultra high voltage direct current,UHVDC)输电线路单端电气量暂态保护方案。对该保护进行了大量仿真分析,计及了雷击干扰、边界上避雷器动作、不同过渡电阻、换相失败故障等因素的影响。仿真结果表明,该保护具有绝对选择性,能可靠有效地保护直流线路全长。展开更多
构建基于极波的特高压直流输电(ultra high voltage DC,UHVDC)线路暂态保护的启动元件、边界元件、雷击干扰识别元件和故障选极元件。线路故障后,保护安装处量测的极波首波头幅值比其对应的极线电压、线模电压和零模电压首波头幅值大,...构建基于极波的特高压直流输电(ultra high voltage DC,UHVDC)线路暂态保护的启动元件、边界元件、雷击干扰识别元件和故障选极元件。线路故障后,保护安装处量测的极波首波头幅值比其对应的极线电压、线模电压和零模电压首波头幅值大,且更为陡峭,故利用极波变化率构造启动判据;利用极波信息熵测度对故障特征进行定量描述、分析和估计来形成区内外故障的识别判据;雷击故障的极波波形远离零轴,而雷击未故障的极波围绕零轴交替变化,故利用短窗内极波采样值直接求均值来构建快速的雷电干扰识别算法;故障极极波与零轴构成的面积远大于非故障极波与零轴构成的面积,故利用正负极的极波与零轴构成的面积之比进行故障选极。时窗取为5 ms,避开控制系统响应对暂态保护的影响。PSCAD仿真结果表明,所提极波暂态量保护原理正确,算法有效。展开更多
Viscous fluid model and potential flow model with and without artificial damping force(f=-μV,μ the damping coefficient and V the local averaging flow velocity) are employed in this work to investigate the phenomenon...Viscous fluid model and potential flow model with and without artificial damping force(f=-μV,μ the damping coefficient and V the local averaging flow velocity) are employed in this work to investigate the phenomenon of fluid resonance in narrow gaps between multi-bodies in close proximity under water waves.The numerical results are compared with experimental data available in the literature.The comparison demonstrates that both the viscous fluid model and the potential flow model are able to predict the resonant frequency reasonably well.However the conventional potential flow model(without artificial damping term) significantly over-predicts the wave height in narrow gaps around the resonant frequency.In order to calibrate the appropriate damping coefficient used for the potential model and make it work as well as the viscous fluid model in predicting the resonant wave height in narrow gaps but with little computational efforts,the dependence of damping coefficient μ on the body geometric dimensions is examined considering the parameters of gap width Bg,body draft D,body breadth ratio Br and body number n(n = 2,3),where Br = BB/BA for the case of two bodies(Body A and Body B) with different breadths of BA and BB,respectively.It was confirmed that the damping coefficient used for the potential flow model is not sensitive to the geometric dimensions and spatial arrangement.It was found that μ∈ [0.4,0.5] may guarantee the variation of Hg/H0 with kh to be generally in good agreement with the experimental data and the results of viscous fluid model,where Hg is the excited wave height in narrow gaps under various dimensionless incident wave frequencies kh,H0 is the incident wave height,k = 2π/L is the wave number and h is the water depth.展开更多
As one of the main aerodynamic noise sources of high-speed trains, the pantograph is a complex structure containing many components, and the flow around it is extremely dynamic, with high-level turbulence. This study ...As one of the main aerodynamic noise sources of high-speed trains, the pantograph is a complex structure containing many components, and the flow around it is extremely dynamic, with high-level turbulence. This study analyzed the near-field unsteady flow around a pantograph using a large-eddy simulation(LES) with high-order finite difference schemes. The far-field aerodynamic noise from a pantograph was predicted using a computational fluid dynamics(CFD)/Ffowcs Williams-Hawkings(FW-H) acoustic analogy. The surface oscillating pressure data were also used in a boundary element method(BEM) acoustic analysis to predict the aerodynamic noise sources of a pantograph and the far-field sound radiation. The results indicated that the main aerodynamic noise sources of the pantograph were the panhead, base frame and knuckle. The panhead had the largest contribution to the far-field aerodynamic noise of the pantograph. The vortex shedding from the panhead generated tonal noise with the dominant peak corresponding to the vortex shedding frequency and the oscillating lift force exerted back on the fluid around the panhead.Additionally, the peak at the second harmonic frequency was associated with the oscillating drag force. The contribution of the knuckle-downstream direction to the pantograph aerodynamic noise was less than that of the knuckle-upstream direction of the pantograph, and the average sound pressure level(SPL) was 3.4 dBA. The directivity of the noise radiated exhibited a typical dipole pattern in which the noise directivity was obvious at the horizontal plane of θ=0°,the longitudinal plane of θ=120°,and the vertical plane of θ=90°.展开更多
文摘高压直流(high voltage direct current,HVDC)输电线路两端的平波电抗器和直流滤波器构成现实的边界元件,对暂态电压高频分量呈带阻传变特性,来自直流线路区外的高频电压信号通过平波电抗器和直流滤波器后被衰减,其能量显著减小,不同频带的高频电压信号小波能量可应用小波变换求得。利用区内、外故障时于保护安装处获得的暂态电压小波能量的显著差异来构造直流输电线路区内、外故障判据;利用故障暂态电压小波变换模极大值,构造启动判据;利用正极和负极暂态电压分别与+800和-800kV的相关系数,构造雷击干扰识别判据;利用两极线极波,构造故障选极判据。给出了特高压直流(ultra high voltage direct current,UHVDC)输电线路单端电气量暂态保护方案。对该保护进行了大量仿真分析,计及了雷击干扰、边界上避雷器动作、不同过渡电阻、换相失败故障等因素的影响。仿真结果表明,该保护具有绝对选择性,能可靠有效地保护直流线路全长。
文摘构建基于极波的特高压直流输电(ultra high voltage DC,UHVDC)线路暂态保护的启动元件、边界元件、雷击干扰识别元件和故障选极元件。线路故障后,保护安装处量测的极波首波头幅值比其对应的极线电压、线模电压和零模电压首波头幅值大,且更为陡峭,故利用极波变化率构造启动判据;利用极波信息熵测度对故障特征进行定量描述、分析和估计来形成区内外故障的识别判据;雷击故障的极波波形远离零轴,而雷击未故障的极波围绕零轴交替变化,故利用短窗内极波采样值直接求均值来构建快速的雷电干扰识别算法;故障极极波与零轴构成的面积远大于非故障极波与零轴构成的面积,故利用正负极的极波与零轴构成的面积之比进行故障选极。时窗取为5 ms,避开控制系统响应对暂态保护的影响。PSCAD仿真结果表明,所提极波暂态量保护原理正确,算法有效。
基金supports from the Natural National Science Foundation of China (Grant Nos.50909016,50921001 and 10802014)support of ARC Discovery Project Program (Grant No. DP0557060)supported by the Open Fund from the State Key Laboratory of Structural Analysis for Industrial Equipment (Grant No. GZ0909)
文摘Viscous fluid model and potential flow model with and without artificial damping force(f=-μV,μ the damping coefficient and V the local averaging flow velocity) are employed in this work to investigate the phenomenon of fluid resonance in narrow gaps between multi-bodies in close proximity under water waves.The numerical results are compared with experimental data available in the literature.The comparison demonstrates that both the viscous fluid model and the potential flow model are able to predict the resonant frequency reasonably well.However the conventional potential flow model(without artificial damping term) significantly over-predicts the wave height in narrow gaps around the resonant frequency.In order to calibrate the appropriate damping coefficient used for the potential model and make it work as well as the viscous fluid model in predicting the resonant wave height in narrow gaps but with little computational efforts,the dependence of damping coefficient μ on the body geometric dimensions is examined considering the parameters of gap width Bg,body draft D,body breadth ratio Br and body number n(n = 2,3),where Br = BB/BA for the case of two bodies(Body A and Body B) with different breadths of BA and BB,respectively.It was confirmed that the damping coefficient used for the potential flow model is not sensitive to the geometric dimensions and spatial arrangement.It was found that μ∈ [0.4,0.5] may guarantee the variation of Hg/H0 with kh to be generally in good agreement with the experimental data and the results of viscous fluid model,where Hg is the excited wave height in narrow gaps under various dimensionless incident wave frequencies kh,H0 is the incident wave height,k = 2π/L is the wave number and h is the water depth.
基金supported by the High-Speed Railway Basic Research Fund Key Project of China(Grant No.U1234208)the National Key Research and Development Program of China(Grant No.2016YFB1200403)+1 种基金the National Natural Science Foundation of China(Grant Nos.51475394&51605397)the Research Project of State Key Laboratory of Traction Power(Grant No.2016TPL_T02)
文摘As one of the main aerodynamic noise sources of high-speed trains, the pantograph is a complex structure containing many components, and the flow around it is extremely dynamic, with high-level turbulence. This study analyzed the near-field unsteady flow around a pantograph using a large-eddy simulation(LES) with high-order finite difference schemes. The far-field aerodynamic noise from a pantograph was predicted using a computational fluid dynamics(CFD)/Ffowcs Williams-Hawkings(FW-H) acoustic analogy. The surface oscillating pressure data were also used in a boundary element method(BEM) acoustic analysis to predict the aerodynamic noise sources of a pantograph and the far-field sound radiation. The results indicated that the main aerodynamic noise sources of the pantograph were the panhead, base frame and knuckle. The panhead had the largest contribution to the far-field aerodynamic noise of the pantograph. The vortex shedding from the panhead generated tonal noise with the dominant peak corresponding to the vortex shedding frequency and the oscillating lift force exerted back on the fluid around the panhead.Additionally, the peak at the second harmonic frequency was associated with the oscillating drag force. The contribution of the knuckle-downstream direction to the pantograph aerodynamic noise was less than that of the knuckle-upstream direction of the pantograph, and the average sound pressure level(SPL) was 3.4 dBA. The directivity of the noise radiated exhibited a typical dipole pattern in which the noise directivity was obvious at the horizontal plane of θ=0°,the longitudinal plane of θ=120°,and the vertical plane of θ=90°.
