A novel method of suppressing the inrush current of transformers by using a series‐connected voltage‐source PWM converter

This paper proposes a novel method of suppressing the inrush current of transformers. A small‐rated voltage‐source PWM converter is connected in series to the transformers through a matching transformer. As the connected PWM converter serves as a resistor for the source current, no inrush phenomena occurs. The required rating of the PWM converter, which serves as the damping resistor for the inrush phenomena, is 1/400 that of the main transformers in single‐phase circuits. In three‐phase circuits, it is 1/900. The basic principle of the proposed method is discussed. Digital computer simulation is implemented to confirm the validity and excellent practicability of the proposed method using the PSCAD/EMTDC. A prototype experimental model is constructed and tested. The experimental results demonstrate that the proposed method can perfectly suppress the inrush phenomena. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 157(4): 56–65, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20174     

龙潭拱坝砼上坝运输方案选择

龙潭拱坝坝高９０ｍ，砼上坝运输是砼施工过程中的中间环节，控制进度的关键，必须因时因地制宜地选择适当的运输机械和运输方案，使砼运输能做到保质、保量、及时和经济，通过论证比较，结合本工程现实情况，砼上坝运输不采用缆机而采用门机方案．     

Air entrainment in fresh concrete with PFA

The results of a study into the influence of PFA on air entrainment in fresh concrete are discussed It is shown that the required dosage of AEA to produce an air content of 5.5 ± 0.5% in a PFA modified concrete mix is two-six times that required in the corresponding neat OPC concrete mix. The dosage of a vinsol based air entraining agent (AEA) required appears to be directly related to the PFA content of the mix. Similar direct relationships were obtained with a range of different PFAs. The dosage of an AEA based on the salt of a fatty acid appears to be sensitive to both PFA and OPC contents. For the type of PFA used, the variability of measured air content or the amount of air retained after continued agitation both indicated that vinsol based AEAs show the highest variability whilst fatty acid based AEAs show low variability. The between batch variability of air content was significantly improved by the addition of PFA regardless of the AEA used.     

混凝土小砌块与普通砖混住宅楼造价分析

指出混凝土小型空心砌块是一种节能型的新型墙体材料。本文从经济角度对该种材料和粘土砖材料进行了实例分析、比较,得出了这种新型材料值得推广使用的结论。     

Damage and deterioration mechanism and curing technique of concrete structure in main coal cleaning plants

Concrete structures in main coal cleaning plants have been rebuilt and reinforced in the coal mines of the Shanghai Da-tun Energy Sources Co. Ltd., the first colliery of the Pingdingshan Coal Co. Ltd. and the Sanhejian mine of the Xuzhou Mining Group Co. Ltd. In these projects, the operating environment and reliability of concrete structures in the main plants of the three companies were investigated and the safety of the structures inspected. Qualitative and quantitative analyses were made on the spe-cial natural, technological and mechanical environments around the structures. On the basis of these analyses, we discuss the long-term, combined actions of the harsh natural (corrosive gases, liquids and solids) and mechanical environments on concrete structures and further investigated the damage and deteriorating mechanisms and curing techniques of concrete structures in the main coal cleaning plants. Our study can provide a theoretical basis for ensuring the reliability of concrete structures in main coal cleaning plants.     

Study on early warning index of spatial deformation for high concrete dam

Owing to the deficiency in early warning for high concrete dam,a formula was established to characterize the deformation behavior of high concrete dam as a whole.The early warning index of spatial deformation was calculated by low probability principle on the basis of the deformation entropy formula proposed.The steps were as follows.Firstly,the probability method was utilized to define the degree of order and degree of chaos for each survey point.Secondly,the weight distribution among the survey points was...     

一种新型气硬冷芯盒树脂砂工艺试验及其在生产中的应用

原砂加入2．5％水溶性酚醛树脂，固化剂为甲酸甲脂，加入量占树脂的30％～40％。先把甲酸甲脂在气体发生器中气化，然后再与40％的压缩空气混合，吹气硬化制芯，最高抗拉强度1．2MPa，抗压强度0．32MPa，发气量12mL／g。生产浇注试验表明：砂芯表面光洁，轮廓清晰，尺寸精确，铸件缺陷少，无毒或低毒，和一般冷硬树脂砂比较，成本降低30％。     

统计过程控制(SPC)在龙滩水电站混凝土生产质量控制中的应用

混凝土生产工艺流程复杂,控制工序多,生产过程除易受系统因素影响外,还受随机因素的干扰较大,生产质量不易控制,本文应用统计过程控制(SPC)在龙滩水电站混凝土生产中的质量控制实践来谈点初浅的认识.     

图像处理建立混凝土有限元模型探讨

针对工程中常用的混凝土材料的不均匀特性,提出了一种基于图像处理技术建立二维混凝土有限元模型的方法.该方法综合图像处理过程中的图像增强、消除噪声和边缘检测技术建立人机对话平台,并结合网格自动划分技术建立非均匀有限元模型.通过一个实例,验证了该方法的有效性.     

移动台车栏板辅助浇筑系统的设计与应用

蒲石河工程下水库大坝顶部混凝土护栏位于坝顶临空边沿,钢筋绑扎和模板支立作业难度大,施工时存在安全隐患。为此,蒲石河工程设计了移动台车栏板辅助浇筑系统并成功应用。实践表明,作业台车设计可靠、安全稳定、操作简便、定位准确、移动方便,保障了施工人员人身安全,节约了成本,加快了工期,提高了模板支立质量,值得类似工程借鉴并推广使用。