Analysing a power transformer’s internal response to system transients using a hybrid modelling methodology

This article presents a novel approach to analysing a power transformer’s internal response to system transients. In this approach a hybrid modelling methodology is adopted which leverages the distinct advantages offered by both Black and Grey Box modelling techniques. The Black Box model of the transformer is used within the EMTP system study environment in order to take advantage of its mathematical flexibility and modelling accuracy. Transients derived from network switching operations within the study can then be used for injection tests within the Grey Box modelling environment. The Grey Box model, which is based upon the physical structure of the transformer, will facilitate analysis of the transformer’s internal voltage response to the external stimulus. A fundamental difference between the approach described in this paper and more traditional approaches is that it does not require prior knowledge of the internal geometry of the transformer. All of the modelling parameters are derived from external tests, nameplate details and an intrinsic understanding of common transformer design principles. This can be a distinct advantage since in most cases a transformer’s design specifications are not readily available outside of the laboratory due to the manufacturer’s intellectual property restrictions. A study of a gas insulated substation within a hydroelectric power plant in Brazil is used to demonstrate the proposed technique.     

箱盖卷耳工艺及模具设计

箱盖边缘卷边类似于普通铰链卷耳,不仅在冲压工艺和模具结构上较为复杂,而且要求模具工作可靠,避免在卷耳过程中出现问题,造成零件报废。文章介绍了汽车工具箱盖成形卷耳工艺及模具设计。     

数字电视机顶盒PSI/SI信息接收和存储方案设计

设计了一种改进型PSI/SI信息接收和存储方案。在接收过程中,通过改进section拼接技术实现section随机且无丢失的快速接收和拼接;在存储过程中,通过三级结构实现PSI/SI同级别信息的联合存储,方便了PSI/SI信息的查询。     

基于Box算法的变电站无功优化

通过预测负荷以及相关的无功综合控制策略,考虑到补偿电容和变压器分接头的动作次数,采用Box算法,在全局范围内求得最优解,对实例的计算表明,此算法能比传统的方法有效地搜索到最优解,实现无功优化.     

A finite segment model for shear lag analysis

A finite segment model is developed to calculate the shear lag effects for box girders with varying depth. Multiple longitudinal displacement functions are used to derive the stiffness matrix and the nodal force vector of the segment element. The shear deformation of the web is taken into consideration. A Perspex glass model of a three-span continuous box girder with varying depth is tested to provide experimental results for verifying the accuracy of the proposed method. The influences of the flange width to span ratio and girder–height ratio upon the shear lag are presented and discussed.     

基于CAK6150P数控车床故障排除实例分析

结合实践中数控车床出现的部分无法换刀现象,将数控机床的故障诊断和排除进行分析与探讨,为出现同类实际问题的解决提供借鉴.     

S135钻杆内螺纹接头胀扣失效分析

本文对某油井发生的Ф127mmS135钻杆内螺纹接头胀扣失效事故进行了调研，并对其胀扣失效原因进行分析。结果表明，钻杆接头的材质符合行业标准要求；钻杆内螺纹接头胀扣失效的原因是外螺纹接头密封台肩面倒角直径过小，井下钻柱扭矩过大。内螺纹接头密封台肩面承受的接触压力超过材料屈服强度，导致内螺纹接头密封台肩面下陷，外螺纹接头密封台肩面进入内螺纹接头镗孔段，致使内螺纹接头发生胀扣失效。     

空腹箱形梁的整体稳定性分析

本文采用等效厚度的方法将加缀板的空腹箱形梁转换为闭口薄壁截面梁.按照乌曼斯基的理论,建立了闭口薄壁梁的侧扭屈曲总势能方程;从总势能驻值原理出发,导出了一个适用于各种荷载与各种支承条件的薄壁截面梁的临界弯矩表达式。     

采集再工程项目管理数据的“黑匣”解决方案

针对数据采集难以保证数据的真实性和实时性问题,从今后软件工程主流趋势的软件再工程入手,提出了嵌入再工程开发支援系统的“黑匣”解决方案,通过记录程序内部变化,自动采集再工程项目管理数据.并介绍了一个应用实例,该实例已获得国家软件著作权,并在多个再工程项目中得到验证,取得了良好效果.     

有线数字机顶盒前端技术发展与应用

有线电视数字化前景广阔，但是机顶盒前端组成则非常灵活，文中对前端的基本原理和几种组成方式进行了论述。介绍了一些主流芯片和解决方案的技术特点。并讨论了前端的发展方向和组成原则。