高海拔超高压绝缘子串雷电冲击伏秒特性

绝缘子串雷电冲击伏秒(V-s)特性曲线对于输电线路防雷设计和并联间隙装置设计具有十分重要的意义。为深入了解该特性,在特高压工程技术(昆明)国家工程实验室对220kV 14片XP-70瓷绝缘子串以及与其干弧距离长度相同的复合绝缘子、500kV 28片XP-70瓷绝缘子串进行了雷电冲击V-s特性试验。试验表明:绝缘子串V-s特性与其干弧距离成正比关系,和材质无关;瓷绝缘子串闪络时,电弧从绝缘子串高压端逐片向上爬升,但在接地端会短接最后2～5片绝缘子,而复合绝缘子则在高压端和接地端之间直接形成放电通道,并可能有次要发展通道存在。     

Adult-child 3D backward face aging model (3D B-FAM)

Face aging has been widely considered in many studies regarding all the potential applications. However, the de-aging known as the rejuvenation or backward modeling has recently received more attention. Previous studies mainly focused on rejuvenating faces from aged adults into young adults using two-dimensional (2D) models. In this work, we propose an extension of a previous 2D adult-child B-FAM into 3D model. This model allows a digital face appearance rejuvenation within a range of [75–3] years old. To evaluate the performances of the proposed approach, first, we proposed two performance evaluation modes, namely: Generic Perception Based and Biometric Verification Mode. Then, the performances have been evaluated over our own 3D database, called Face Time-Machine database constructed using 75 females and 70 males, leading to 500 textured surface meshes. Finally, results show that they are perceptually satisfying and system performance increases by using the faces obtained from our model.     

Hybridization of g-C3N4 quantum dots with 1D branched TiO2 fiber for efficient visible light-driven photocatalytic hydrogen generation

The hybrid 1D branched TiO₂ loaded with g-C₃N₄ QDs was successfully fabricated that plays a significant role in photocatalysis. The 1D branched TiO₂ prepared by electrospinning followed by alkali-hydrothermal process, and g-C₃N₄ QDs were grafted over it by a chemical vapor deposition method. The composite display enhancement in photocatalytic hydrogen evolution is about 10.57 mmol. g⁻¹.h⁻¹ in comparison to the g-C₃N₄ sample that only produces 0.32 mmol. g⁻¹.h⁻¹ while the HBTiO₂ sample evolved a negligible amount of hydrogen under visible light. The composite sample shows quantum efficiency for HER at 420 nm light is 18.6% that is much higher than the other two samples. The specific surface area of the composite sample is 92.39 m²g^-1 that is about 13 times more than bulk g-C₃N_4. The bandgap of HBTiO₂/g-C₃N₄ QDs, g-C₃N₄, and HBTiO₂ samples calculated as 2.71 eV, 2.67eV, and 3.24eV, respectively. The TRPL spectra imply that the duration of the lifetime of composite becomes longer which effectually overwhelm the electron-hole recombination. The 1D branched TiO₂ fiber reduces the charge recombination by fast transfer of electron while g-C₃N₄ QDs facilitate the visible light absorption by improving the optical properties. The formation of the type II heterostructure system remarkably promotes the separation and transfer of electron holes and facilitates the photo-reduction reaction.     

电力系统小干扰稳定实时风险评估方法

为实时反映当前电力系统小干扰稳定性状况,建立了小干扰稳定性实时风险评估指标,提出了电力系统小干扰稳定实时风险评估方法。评估模型中,在当前运行状态或者关键线路N-1状态下,利用特征值分析方法,以阻尼比0.05作为阈值判断小干扰稳定性;计及输电线路实时故障率计算关键线路N-1状态下小干扰失稳概率。在小干扰失稳后果评估中,利用参与因子筛选调整节点,以控制代价最小化为目标,依据阻尼比灵敏度,迭代计算调整节点控制量,最终协调所有弱阻尼振荡模式控制量,生成综合优化控制方案,计算控制代价作为后果指标;以华中电网某一时间断面的数据为例,验证了该风险评估方法的有效性。     

交、直流电压下复合绝缘子和瓷绝缘子的自然积污试验

利用位于北京市西北的自然积污试验站,研究了交流与直流电压下复合绝缘子和XP-70、XWP-70型瓷绝缘子的积污特点及积污量关系。在该站条件下,不同绝缘子污秽差异主要在绝缘子下伞面;交流电压下,积污期内复合绝缘子上伞面积污速率略高于瓷绝缘子上伞面,下伞面积污速率是瓷绝缘子下伞面的2倍以上。复合绝缘子下伞面的直流与交流积污比>5,瓷绝缘子下伞面的直流与交流积污比>10。大、小雨量下绝缘子下伞面受到两种不同方式的自清洗。复合绝缘子下伞面自清洗略受憎水性影响而削弱。直流与交流电压下,积污3a与积污1a的复合绝缘子下伞面污秽比值分别约为2.2和1.4,上伞面污秽相差不大。     

基于广域测量系统的电力系统稳定控制

近年随着电网规模扩大、区域系统互联,电力系统出现一些现有方法难以解决的稳定问题,例如,如何持久有效地抑制区间低频振荡等,而同步相量测量技术的发展及广域测量系统(WAMS)的建设为此提供了新的手段.重点结合实际系统应用说明了当前世界上WAMS发展现状及其在电力系统保护与稳定控制中的应用实例.首先,介绍了PMU及WAMS的基本原理与历史发展过程;其次,在详细说明美国与中国WAMS发展现状的基础上,概述了各主要WAMS的规模和PMU的性能水平.最后,从非连续控制及连续反馈控制2个方面介绍了WAMS在电力系统稳定控制中的实际方案.     

One-step synthesis of unique catalyst Ni9S8@C for excellent MOR performances

A novel Ni₉S₈/C electrocatalyst for methanol oxidation reaction (MOR) is synthesized by a simple, cost-effective and one-pot strategy. The electrocatalyst Ni₉S₈ composed of micro and nanoparticles encapsulated inside carbon layers serves as carbon-supporter and fast ion and electron mobilization through the Ni₉S₈/C support materials. The sizes of Ni₉S₈/C nanoparticles range from 2.4 to 7.99 nm, reveals large surface area availability with plenty of active sites for electro-oxidation of methanol. The oxidation performance of electrocatalyst is determined in different solution of methanol and alcohol at various scan rates. At a scan rate of 50 mV s⁻¹, the Ni₉S₈/C catalyst delivers total 52 mA cm⁻² current density for 1.75 V potential (vs RHE) for 1 M KOH and 0.5 M methanol. The electrocatalyst shows low Rct circle and linear chronoamperometric graph for 5000 s, which demonstrate the outstanding stability of the electrocatalyst for methanol electro-oxidation reaction.     

A design method of nonlinear optimal predictive controller for thyristor controlled series compensation

In this paper, a design method of thyristor controlled series compensation (TCSC) controller with closed-form analytic solution control law is presented so as to improve transient stability and dynamic performance of power systems, on the basis of nonlinear optimal predictive control theory. The control scheme is robust and considers uncertainty of power systems. The stability of the closed-loop system is guaranteed by the control law which does not require on-line optimization and the huge calculation burden is avoided, besides, all input variables can be obtained locally. The simulation results demonstrate that the controller may improve transient stability and dynamic performance of power systems significantly.     

A simulated model for a once-through boiler by parameter adjustment based on genetic algorithms

In this paper based on the physical rules, thermodynamics principles and energy mass balance, the simulation models are developed and applied to electrical power generating plants in order to characterize the essential dynamic behavior of the boiler subsystems and to use the corresponding models for the power plant processes. These models are developed for a sub-critical once through Benson type boiler based on the experimental data obtained from a complete set of field experiments. An optimization approach based on genetic algorithm (GA) is executed to estimate the model parameters and fit the models response on the real system dynamics. Comparison between the responses of the corresponding models with the response of the real plants validates the accuracy and performance of modeling approach. A similar comparison between the responses of these models with linear parametric models shows the effectiveness and feasibility of the developed model in term of more accurate and less deviation between the responses of the models and the corresponding subsystems.     

基于正规形理论的多馈入交直流输电系统非线性模式分析

传统的特征根分析法不能揭示电力系统的非线性相关作用.正规形理论将非线性系统通过坐标变换,使得原系统与一个线性系统二阶或更高阶等价.将该方法应用到电力系统稳定分析中,既保留了小信号法的优点,又考虑了不同振荡模式间的非线性作用,适用于系统大扰动后的低频振荡特性分析.在对一双馈入交直流并联系统建立动态方程的基础上,运用正规形理论,分析了多馈入交直流系统低频振荡模式的非线性相关作用.结果显示,系统中各种模式是相互影响的,不同运行方式下影响程度也不相同,当系统重载且直流带调制方式下时,区间振荡模式与直流调制模式间的非线性作用最强.时域仿真验证了这一结果.