为提高母线保护的动作速度,根据行波传输理论,提出一种行波波形积分式快速母线保护方法。当母线故障时,在所有出线上检测到的初始行波均来自于线路的背后,是正向行波;而某条出线发生故障时,在所有非故障线路上检测到的初始行波是正向行...为提高母线保护的动作速度,根据行波传输理论,提出一种行波波形积分式快速母线保护方法。当母线故障时,在所有出线上检测到的初始行波均来自于线路的背后,是正向行波;而某条出线发生故障时,在所有非故障线路上检测到的初始行波是正向行波,而故障线路上检测到的初始行波是反向行波。在故障后特定时间内对各条出线上的方向行波进行积分运算,根据正反向行波积分值的比值大小识别故障方向。综合分析所有出线的故障方向,可识别母线是否发生故障。利用PSCAD/EMTDC构建了500 k V母线模型,仿真结果表明:所提方法鲁棒性强、动作快速、可靠性高,其性能基本不受故障电阻、故障初始角、开关操作等的影响,有望应用于实际的电力工程中。展开更多
Turbulent open channel flows subjected to the control of a spanwise traveling wave have been investigated by means of Direct Numerical Simulation （DNS）. The objective of this study is to reveal the response of the n...Turbulent open channel flows subjected to the control of a spanwise traveling wave have been investigated by means of Direct Numerical Simulation （DNS）. The objective of this study is to reveal the response of the near-wall and surface-influenced turbulence to the spanwise traveling wave control. Three typical frequencies of the spanwise traveling wave, i.e., high-, middle- and low-frequency, corresponding to the exciting periods at 25, 50 and 100, are considered to study the turbulence dynamics in the wall and surface regions. To elucidate the behaviors of turbulence statistics, some typical quantities, including the mean velocity, velocity fluctuations and the structures of turbulence fluctuations, are exhibited and analyzed.展开更多
In order to get the exact traveling wave solutions to nonlinear partial differential equation, the complete discrimination system for polynomial and direct integral method are applied to the considered equation. All s...In order to get the exact traveling wave solutions to nonlinear partial differential equation, the complete discrimination system for polynomial and direct integral method are applied to the considered equation. All single traveling wave solutions to the equation can be obtained. As an example, we give the solutions to (3 + 1)-dimensional breaking soliton equation.展开更多
高压直流(high voltage direct current,HVDC)输电线路行波保护及测距装置的分析、整定主要依赖于数值仿真方法,难以反映行波过程的物理本质和影响因素,也无法进行整定计算。分析了直流线路行波在故障点及包含直流滤波器的线路末端的折...高压直流(high voltage direct current,HVDC)输电线路行波保护及测距装置的分析、整定主要依赖于数值仿真方法,难以反映行波过程的物理本质和影响因素,也无法进行整定计算。分析了直流线路行波在故障点及包含直流滤波器的线路末端的折反射规律,在此基础上推导了基于无畸变传输线模型的行波解析解,用以研究直流滤波器、故障电阻和故障位置对直流线路行波的影响。研究表明:直流滤波器使行波波头由阶跃波变成衰减的振荡波,从而使其变化率和幅值都减小;过渡电阻主要影响行波波头的幅值大小。基于该解析表达式计算而得的行波变化率可用于实际工程中的行波保护整定。在EMTDC仿真软件中,结合中国某实际直流系统建立仿真模型,大量的仿真结果验证了所得出的解析解以及分析结果的正确性和有效性。展开更多
文摘为提高母线保护的动作速度,根据行波传输理论,提出一种行波波形积分式快速母线保护方法。当母线故障时,在所有出线上检测到的初始行波均来自于线路的背后,是正向行波;而某条出线发生故障时,在所有非故障线路上检测到的初始行波是正向行波,而故障线路上检测到的初始行波是反向行波。在故障后特定时间内对各条出线上的方向行波进行积分运算,根据正反向行波积分值的比值大小识别故障方向。综合分析所有出线的故障方向,可识别母线是否发生故障。利用PSCAD/EMTDC构建了500 k V母线模型,仿真结果表明:所提方法鲁棒性强、动作快速、可靠性高,其性能基本不受故障电阻、故障初始角、开关操作等的影响,有望应用于实际的电力工程中。
基金Project supported by the National Natural Science Foundation of China (Grant Nos 90405007, 10772173 and 90605005)the Program for Cheung Kong Scholars and Innovative Research Team in the University+1 种基金the Science and Technology Innovative Foundation of the Chinese Academy of Sciences (Grant No CXJJ-237)the Anhui Provincial Excellent Young Scholars Foundation (Grant No 08040106826)
文摘Turbulent open channel flows subjected to the control of a spanwise traveling wave have been investigated by means of Direct Numerical Simulation （DNS）. The objective of this study is to reveal the response of the near-wall and surface-influenced turbulence to the spanwise traveling wave control. Three typical frequencies of the spanwise traveling wave, i.e., high-, middle- and low-frequency, corresponding to the exciting periods at 25, 50 and 100, are considered to study the turbulence dynamics in the wall and surface regions. To elucidate the behaviors of turbulence statistics, some typical quantities, including the mean velocity, velocity fluctuations and the structures of turbulence fluctuations, are exhibited and analyzed.
文摘In order to get the exact traveling wave solutions to nonlinear partial differential equation, the complete discrimination system for polynomial and direct integral method are applied to the considered equation. All single traveling wave solutions to the equation can be obtained. As an example, we give the solutions to (3 + 1)-dimensional breaking soliton equation.
文摘高压直流(high voltage direct current,HVDC)输电线路行波保护及测距装置的分析、整定主要依赖于数值仿真方法,难以反映行波过程的物理本质和影响因素,也无法进行整定计算。分析了直流线路行波在故障点及包含直流滤波器的线路末端的折反射规律,在此基础上推导了基于无畸变传输线模型的行波解析解,用以研究直流滤波器、故障电阻和故障位置对直流线路行波的影响。研究表明:直流滤波器使行波波头由阶跃波变成衰减的振荡波,从而使其变化率和幅值都减小;过渡电阻主要影响行波波头的幅值大小。基于该解析表达式计算而得的行波变化率可用于实际工程中的行波保护整定。在EMTDC仿真软件中,结合中国某实际直流系统建立仿真模型,大量的仿真结果验证了所得出的解析解以及分析结果的正确性和有效性。
