Impact of HVDC line on the convergence property of AC/DC power flow calculation

This paper explores the impact of HVDC line on the convergence property of AC/DC power flow calculation. Firstly, the model of AC/DC power flow computation is constructed, including unified method and alternate iterative method. Then, an improved Levenberg–Marquardt (LM) method with line search technique is developed to solve the nonlinear equations of AC/DC power flow. To test the convergence property of the proposed method, LM method with trust region technique and Newton method are also employed. The researches on the impact of heavy DC transmission power and multiple HVDC lines on the convergence property of AC/DC power flow calculation are made on a modified IEEE 118-bus AC/DC hybrid test system. Simulation results show that the developed method under the model of alternate iterative method is superior to other methods under different models in convergence property. For the influence of heavy DC transmission power on the convergence property, it is improved by the new parameter configuration of DC transmission line firstly and adding proper new shunt capacitor on the weak nodes secondly; for the influence of multiple DC transmission lines on the convergence property, it can also be improved by the change of control mode firstly and adding new shunt capacitor secondly, which are based on the least square solution obtained by proposed method under the model of alternate iterative method.     

Single and two-phase flow modeling and analysis of a coaxial vacuum tube solar collector

In this paper, an analytical steady state model is developed to study the thermal performance of an individual vacuum tube solar collector with coaxial piping (direct flow type) incorporating both single and two-phase flows. A system of equations which describe the different heat transfer mechanisms and flow conditions was established, discretised, and solved in an iterative manner. For the case of good vacuum condition (10^?5 mb) the calculated efficiency curve for single phase flow deviates significantly from the experiments with increasing collector temperature, but agrees well for the case of gas conduction inside the glass envelope at very low pressure (?1 mb) due to the corresponding increase in overall heat loss coefficient (U-value).For two-phase flow, the occurrence and propagation of flow boiling and condensation inside the collector piping under saturated condition is hypothesized. The modeling results indicate that for all-liquid-single-phase fluid flow, the collector efficiency decreases with decreasing mass flow rate. Once the fluid reaches the boiling point at a certain mass flow rate, no significant reduction in efficiency is observed anymore, which is in accordance with the experimental study.     

电力系统规划数据平台的数据设计

目前,常用电力系统规划应用软件没有全面、规范的电力系统规划基础数据平台,采用面向对象分析方法和统一建模语言建立电力系统规划数据模型,实现了类设计到数据库表设计的转换,探讨通用励磁系统数据模型和自关联数据模型的设计.应用表明,电力系统规划数据平台信息全面,可扩展性强,能够提高规划工作水平和效率.     

基于故障区域局部迭代的工程实用化新能源短路电流计算

新能源快速发展,正在由辅助电源向主力电源过渡.现有新能源工程短路电流计算存在两大问题.一是用1.2～2倍额定电流表征新能源故障特性,过度简化导致计算精度差,难以满足保护要求;二是现有短路电流整定计算软件不支持迭代,因而无法根据节点电压变化而更新新能源故障电流,体现其压控电流源特性.针对该问题,首先,基于新能源的故障特性精细化解析模型,结合现场故障录波数据,构建满足工程实用计算要求的电压电流映射关系;然后,根据电网故障后节点电压跌落程度和节点之间的连接关系划分故障区域,并在故障区域内依据新能源的工程实用化计算公式进行局部迭代计算来求解网络的节点电压和短路电流,从而避免了全局迭代可能带来的收敛性问题,同时也缩短了计算时间;最后,通过工程计算软件验证了所提方法的计算效果.     

基于动态小波变换的电力系统故障信号分析

提出了基于动态小波变换的电力系统故障分析方法,既充分利用了小波变换在电力系统故障信号分析中的优点,又克服了分析中傅里叶算法的不足。该方法简单、可靠,便于形成实时软件,对于提高电力系统故障检测水平和保护性能具有重要意义。     

应用附件系统提高复合支柱绝缘子的干闪络电压

分析了传统绝缘子在外绝缘方面存在的一些问题,提出了应用附件系统来提高传统绝缘子的外绝缘性能的解决方法,针对复合支柱绝缘子进行了干闪络的试验,试验结果表明:在不增加绝缘子长度的情况下,应用附件系统可提高其干闪络电压。     

1000 MW汽轮发电机转子绕组匝间短路故障的诊断与分析

以某电厂1000 MW汽轮发电机在运行过程中发现转子轴振动异常为例,对转子绕组匝间短路故障进行了诊断与分析.对该转子进行了降速过程和盘车状态的交流阻抗及损耗试验,并进行了盘车状态的RSO试验.分析了试验数据诊断与动态下的判断互相矛盾的原因.阐明了转子在运行中振动幅度明显与负荷的变化呈正相关性,并由此导致匝间存在短路隐患.建议及时关注转子的振动幅值和负荷变化的关系,以便及时应对转子绕组匝间出现的短路故障.     

换流变压器直流偏磁的保护判据研究

阐述直流偏磁对换流变压器和直流系统的影响和危害,运用电磁暂态仿真程序(Electro Magnetic Transient in DC System,EMTDC)对国际大电网会议(International Conference on Large HV Electric System,CIGRE)直流输电标准测试系统正...     

New low temperature electrolytes with thermal runaway inhibition for lithium-ion rechargeable batteries

This paper describes a low temperature electrolyte system for lithium-ion rechargeable batteries. The electrolyte exhibits high ionic conductivity, good electrochemical stability and no exothermic reaction in the presence of lithium metal. The system features a low lattice energy lithium salt in a specific mixture of carbonate solvents and a novel thermal runaway inhibitor.     

基于光传感复合绝缘子智能监测技术探讨

探讨了一种基于光传感复合绝缘子智能监测技术,该技术在复合绝缘子的芯棒基体内植入布拉格光栅构成智能芯棒结构,这种结构能在线检测复合绝缘子内部温度与应力的变化,从而可以实时监测复合绝缘子的运行状态,并判断出复合绝缘子内部缺陷,实现对在线运行复合绝缘子的状态评估及寿命预测。