Research and application of a power-flow-calculation method in multiterminal VSC-HVDC power grid

For demonstrating a multiterminal voltage-source converter (VSC)-based high-voltage DC (HVDC) (VSC- HVDC) project, this study puts forward a technical route for calculating the power flow in a 500-kV VSC-HVDC power grid in comparison with that of an AC power grid. The Jacobian matrix used in the power-flow calculation was deduced through methods such as Newton-Laphson iteration and Taylor series expansion. Further, the operation effect of power- flow calculation on a true bipolar VSC-HVDC power grid was analyzed briefly. The elements of the Jacobian matrix corresponding to VSC were studied under the mode of droop control and the control strategy of VSC-HVDC power grid was analyzed in detail. The power-flow calculation model for VSC-HVDC power grid of the master-slave control mode was simplified using the PQ decomposition method of the power-flow calculation of an AC power grid. Moreover, a four-terminal model of the Zhangbei VSC-HVDC demonstration project was established and tested on MATLAB. The simulation results under two kinds of operating conditions were analyzed and compared to the results of BPA; the deviation between the power-flow results was studied. The results show that the proposed calculation method can provide a feasible support for calculating the power flow in VSC-HVDC grids.     

Validity of facial features’ geometric measurements for real-time assessment of mental fatigue in construction equipment operators

Operating construction equipment for extended periods of time may lead to mental fatigue and, as a result, an increased risk of human error-related accidents and jeopardized health problems for the operators. Therefore, to limit the risk of accidents and protect operators' wellbeing, their mental fatigue must be monitored reliably and in real time. Recently, many invasive technologies have been employed to alleviate this problem, but they entail the wearing of physical sensors, which may instigate irritation and discomfort. This study proposes a non-invasive mental fatigue monitoring method using geometric measurements of their facial features that does not require the operators to wear sensors on their body. The study further validates the proposed method by comparing it with wearable electroencephalography (EEG) technology to establish its ecological validity for construction equipment operators. To serve the purpose, a one-hour excavator operation by sixteen construction equipment operators was conducted on a construction site. Ground truth, brain activity using wearable EEG, and geometric measurements of facial features were extracted and analyzed at the baseline and every 20 min for one hour. A considerable temporal variation was found in the reported metrics (eye aspect ratio, eye distance, mouth aspect ratio, face area, and head motion) and were significantly correlated with ground truth and EEG metric. Furthermore, the brain visualization pattern obtained from EEG was also associated with the variations in the facial features. The findings of the study reveal that construction equipment operators’ mental fatigue can be monitored non-invasively using geometrical measurements of facial features.     

高压直流换流阀均压电极的结垢机理研究

目的 通过研究换流阀冷却系统均压电极结垢机理,分析结垢的过程、影响因素、形成规律,总结结垢的根本原因,再根据分析结论提出均压电极腐蚀结垢的综合整治措施,形成改进技术方案。方法 先通过文献分析国内外均压电极研究进展并进行总结,找出均压电极结垢的相关影响因素,通过试验验证,明确均压电极结垢的主要过程和影响结垢的主要因素,最后根据试验结果提出合理的抑制或减轻结垢的措施。结果 均压电极结垢的主要影响因素是铝制散热器的电化学腐蚀及流体冲刷腐蚀,腐蚀产物在均压电极部位汇聚、沉积,导致结垢。结垢过程为：散热器内表面发生的化学腐蚀以及流体喘振造成的磨损腐蚀二者协同,相互加强,致使铝元素转化为离子形态进入循环系统冷却介质中,并在均压电极电场作用下吸附至电极表面,从而在电极表面形成结垢。结论 均压电极结垢与水冷系统的电化学腐蚀和流体冲刷有关,采用深度除盐水质精处理的方式去除冷却水中的致垢离子,能有效减缓均压电极的结垢。     

采用波形识别的直流50Hz保护优化改进策略

结合近几年来南方电网多次出现的变压器空投涌流引起直流50 Hz保护动作事件,仿真研究了励磁涌流、和应涌流及故障电流波形特征差异性,在不降低保护灵敏度的原则下,提出了一种基于波形识别的直流50Hz保护优化改进策略,并在高压直流PSCAD/EMTDC控制保护仿真模型的基础上结合优化改进策略自定义创建直流50Hz保护闭锁模型,从交流系统强度变化、换流变压器空载合闸角变化、换流变压器铁芯剩磁变化三个角度对所提出的优化策略进行仿真验证。结果表明,所提出的基于波形识别的直流50Hz保护优化改进策略能正确地实现直流50 Hz保护的闭锁和解锁,在不影响直流系统安全稳定运行的情况下很好地解决了变压器空投涌流引起直流50Hz保护误动的问题。     

SF6气体湿度计算优化与应用

介绍了露点法测量气体湿度的原理,研究并优化了SF6气体湿度计算方法,并将研究所得方法应用于生产实际.通过对比应用情况发现,利用EXCEL、MATLAB、FrontPage等软件实现优化的计算方法,优于目前采用的手动查找并计算的方法,而且通过对比几种优化后的计算方法,得出用FrontPage实现的查找并计算方法具有占用资源少、界面明了等优点.     

Hydrocarbon flame inhibition by C6F12O (Novec 1230): Unstretched burning velocity measurements and predictions

This study experimentally and numerically determined the unstretched laminar burning velocity of premixed CH₄-air and C₃H₈-air flames with added C₆F₁₂O (Novec 1230). High-speed shadowgraphy of spherically expanding flames provided the burning velocity as a function of stretch, which was extrapolated to zero-stretch conditions using non-linear methods. Unstretched burning velocities predicted using a recently assembled kinetic mechanism were generally in good agreement with the measurements, but tended to have poorer agreement for highly-inhibited very lean flames. To benchmark the performance of C₆F₁₂O, measured burning velocities were compared to previously measured burning velocities of premixed flames inhibited by CF₃Br (Halon 1301). The two agents provided similar reductions in the burning velocity of rich flames, whereas CF₃Br provided greater reductions when added to stoichiometric and lean flames. Lastly, experiments and simulations showed the influence of water vapor on the burning velocity of lean C₃H₈-air flames with added C₆F₁₂O. The presence of water vapor in the oxidizer increased the burning velocity by up to 23% when the fluorine to hydrogen ratio of the reactant mixture was greater than unity.     

变压吸附(PSA)废气的回收利用

针对变压吸附中的逆放气与解析气的排放污染环境,回收占用空间大,作者从实际工艺出发,考虑上下游装置实际情况,本装置存在废气回收利用的可能,经过实际改造后投用效果明显,既解决了废气污染,又实现了节能减排的目的.     

国内常见ABS产品对比剖析

收集了国内市场上常见的几种ABS产品,通过力学分析以及组成、结构分析,总结出各种产品特点及适用领域。考察组成ABS的接枝物含量以及SAN分子质量、氮含量对ABS性能的影响。发现苯乙烯组分对ABS产品的流动性影响较大,丙烯腈组分对拉伸强度、冲击强度影响较大。     

Two online dam safety monitoring models based on the process of extracting environmental effect

In this paper, the complex relationship between environmental variables and dam static response is expressed using composition of functions, including nonlinear mapping and linear mapping. The environmental effect and noise disturbance is successfully separated from the monitoring data by analysis of the covariance matrix of multivariate monitoring data of dam response. Based on this separation process, two multivariate dam safety monitoring models are proposed. In model I, the upper control limits (UCLs) are calculated by performing kernel density estimation (KDE) on the square prediction error (SPE) of the offline data. For new monitoring data, we can judge whether they are abnormal by comparing the newly calculated SPE with the UCL. When abnormal data are detected, the SPE contribution plots and the SPE control chart of the new monitoring data are jointly used to qualitatively identify the reason for the abnormalities. Model II is a dam monitoring model based on latent variables that can be calculated from the separation process of the environmental and noise effects. The least squares support vector machines (LS-SVMs) model is adopted to simulate the nonlinear mapping from environmental variables to latent variables. The latent variables are predicted, and the prediction interval is calculated to provide a control range for the future monitoring data. The two monitoring models are applied to analyze the monitoring data of the horizontal displacement and hydraulic uplift pressure of a roller-compacted concrete (RCC) gravity dam. The analysis results demonstrate the good performance of the two models.     

轨道交通直流1500V系统保护及双边联跳调试

根据上海轨道交通的实际情况，简要介绍了轨道交通直流牵引系统的原理和构成，直流牵引系统继电保护的构成，双边联跳构成、原理以及双边联跳的实际构成方式，并对双边联跳的调试提出了一些方案和建议。