上旋转电磁挂梁起重机回转机构电动机计算

上旋转电磁挂梁起重机的回转机构可采用滚动轴承式回转支承,文中简要介绍了采用此回转机构的起重机小车及吊具,提出了回转机构电动机的计算方法,并探讨了这种方法在实际应用中发现的问题及解决措施。

答《也谈电动机启动计算及校验》一文

发表在《建筑电气》 2018年第7期的《也谈电动机启动计算及校验》一文,对《工业与民用供配电设计手册》(第4版)和《电动机启动时电压暂降计算法之考证与改进》一文提出诸多质疑。本文澄清了其中似是而非的论点,反驳了对手册有失公正的评价,并提出一些改进意见和有待探讨的问题。

也谈电动机启动计算及校验

《建筑电气》2016年第6期"电动机启动时电压暂降计算法之考证与改进"一文以及《工业与民用供配电设计手册》(第4版)均指出了原设计手册关于电动机启动计算公式存在的错误,并提出新的计算公式。笔者经过推演发现,新的计算公式依旧存在一些不足,本文就此进行分析并提出一些笔者的见解。

机构电动机功率计算方法对比

依据GB/T 3811—2008《起重机设计规范》所提供的机构电动机功率计算及选择方法,对同一起升机构分别计算、选择和对比,借此探讨GB/T 3811—2008《起重机设计规范》中关于机构电动机功率计算及选择方法的差异,并提出相应的建议。

电动机启动压降精确计算及比较

以《工业与民用供配电设计手册》第四版电动机启动压降计算公式作为切入点,引出相对精确的电动机启动压降计算公式。通过多种计算方法比较,发现由于手册中给出的计算公式过度简化,所算得的结果与精准计算、仿真结果相差2%左右。这偏差对于有较高计算精准度要求的设计选型是不利的。因此通过比较,引出较为精准的计算方法,以代替手册中给出的电动机启动压降计算公式。

非正弦输入下异步电机损耗计算与分析

当电机的供电电压呈非正弦时,利用传统电机等效模型分析能耗关系的方法因缺乏明确的物理意义而不再适用。针对上述问题,本文分析了电机等效模型的建立与适用条件,以及异步电机的功率关系,在此基础上提出了将非正弦供电电压等效为正弦供电电压的能量等效方法,进而通过电机等效模型计算电机内部损耗。利用Matlab工具编制了非正弦情况下电机损耗计算软件,算例分析验证了该方法的有效性和软件的正确性。

有关工程实用计算口诀在教学中的应用

在电气专业理论教学中,理论计算必须掌握一定的理论知识,一些计算公式,花费大量的计算时间,而掌握工程实用计算口诀,往往比较简便,得出一种把有关工程实用计算口诀,应用到教学中的教学方式,给学生成就感,激发学生的学习的热情在有限的时间内让学生学到更多的知识。

矿井空压机房内变压器的选择

矿井空压机房内设10kV变配电设备为空气压缩机和空压机房周边单体建筑配电,结合母线电压、电动机电压波动计算以及变压器负荷率、过载能力的计算,合理确定变压器容量。

Performance Analysis of PMSM Equations Computation

The paper deals with the comparison of three different digital devices used for the computing of permanent magnet synchronous motor （PMSM） model. Model is used for virtual high frequency injection method （VHFIM） sensorless control, where injection and acting voltages are virtual ones. For computing the whole PMSM model, differential equations are used. The paper is focused on performance analysis of computing speed and accuracy of field-programmable gate array （FPGA） device, digital signal controller and Power PC microcontroller and results are compared.

A Transductive Scheme Based Inference Techniques for Network Forensic Analysis

Network forensics is a security infrastructure,and becomes the research focus of forensic investigation.However many challenges still exist in conducting network forensics:network has produced large amounts of data;the comprehensibility of evidence extracting from collected data;the efficiency of evidence analysis methods,etc.To solve these problems,in this paper we develop a network intrusion forensics system based on transductive scheme that can detect and analyze efficiently computer crime in networked environments,and extract digital evidence automatically.At the end of the paper,we evaluate our method on a series of experiments on KDD Cup 1999 dataset.The results demonstrate that our methods are actually effective for real-time network forensics,and can provide comprehensible aid for a forensic expert.

Decision-tree induction from self-mapping space based on web

An improved decision tree method for web information retrieval with self-mapping attributes is proposed.The self-mapping tree has a value of self-mapping attribute in its internal node,and information based on dissimilarity between a pair of mapping sequences.This method selects self-mapping which exists between data by exhaustive search based on relation and attribute information.Experimental results confirm that the improved method constructs comprehensive and accurate decision tree.Moreover,an example shows that the self-mapping decision tree is promising for data mining and knowledge discovery.

Research on hydraulic wind turbine semi-physical simulation platform

According to a research on the 30kVA simulation experimental platform of hydraulic wind tur- bine, its basic structure, composition and operation principle are expounded in this paper. An in- verter motor is used to simulate the wind turbine, while a similarity calculation method is applied be- tween the small and large wind turbine. A fixed displacement pump-variable motor closed loop is used as the main transmission system, and a self-excited synchronous generator generates electricity through the grid connection. The experiment and simulation study on the speed and power control of the hydraulic wind turbine is conducted, based on the experimental platform, thus correctness and progressiveness of the experiment platform is further verified. The experimental platform study lays a foundation for further research on the characteristics of hydraulic wind turhln~

The basic design of a thermal computer

This paper presents a new thermal computer, which is driven by heat current and not electricity current. The basic thermal logic gate, such as thermal logic AND gate. thermal logic NOT gate, thermal logic OR gate are discussed in this paper. Compared with electronic computer, it can work at some special environment, such as high temperature and high pressure Consequently, the heat computer is not only a new special computer, but also a lot of new heat computation cell or device could be invented in the future. The thermal computer and control device are a new thermal energy machines powered by heat energy, it is significant for the environmental protection, energy usage and developed and new discipline development.

Megabots Team： A Team for the Category Sumo Autonomous 3 kg

This paper deals with a method for building a mobile robot in order to transform the material into a practical guide for beginners in the study of mobile robotics. The project is divided into layers that can define the topics related to the areas of knowledge that will be used in carrying out the project. These areas are the mechanics, electronics and computing system. The mobile robot named Fable was developed accordingly to this method. It is composed by two active wheels, each one driven by DC motor with a high torque and a transmission system containing two spur gears. It has three sonars for detection of the opponent and two infrared sensors to detect a line and an Arduino Uno board is used to control all the actions of the robot.

Bench for Vibration Study in an Unbalanced Motor Using Arduino

Part of the difficulty in engineering education is to achieve aggregate theoretical knowledge to practice what therefore discourages the student. Trying to alleviate this difficulty, practical problems are created to encourage students to apply their knowledge in different ways; these problems can be computational order, resolved by programs through simulation, or physical, with the realization of models, prototypes, benches or interactive platforms with visual practical approach. From this, it was proposed to students of the Federal University of Pardi--Campus Tucurui through the Electric Power Systems and Mechanics Research Group, in order to apply knowledge arising from multidisciplinary fields of engineering in the construction of a prototype with reused materials and low cost enabling studies and analysis of vibrations in unbalanced motors. This system features an open source prototyping embedded platform Arduino to read values from the sensors used： accelerometers and potentiometers coupled to the engine, aiming to collect values and vary the supply voltage. The results are read by Arduino and computationally processed to be printed on an LCD display. Therefore, the aim of this is to provide an accessible way using simple techniques a prototype linking the theoretical and practical knowledge as the system of the bench that performs vibration analysis in an unbalanced motor interactively, and encourage research and development technologies in the Amazon region.

Transitional Recovery Voltages at Capacitive Currents Switching-off by Vacuum and SF6 Circuit-Breakers

Results of calculation the recovery voltages conditioned by capacitive currents switching-off by high voltage vacuum and auto-compression （SF6） circuit-breakers are presented in the article. The purpose of research was evaluating the maximum values of recovery voltages and also studying the dependence of recovery voltages on some influencing factors, especially on type of circuit-breaker presented in numerical models with its dielectric strength restoration law, chopping current and operation time. The research was carried out with using computer simulation.

Building Effects on a Horizontal-Axis Micro Wind Turbine： Experimental and Fluid-Dynamic Analysis

In this work, the efficiency ofa 1 kWp horizontal-axis wind turbine which is installed on the roof of the engineering building at the University of Salento has been evaluated, by means of CFD （computational fluid dynamic） and experimental data. Particularly, the influence of the building on the micro wind turbine performance has been studied and the numerical results （wind velocity fields and turbulence intensity above the building） have been compared with the experimental data collected over a period of three years. The results have shown that horizontal-axis wind turbines suffer from wake effect due to buildings, therefore, best sites in urban area have to be identified by a careful fluid dynamic analysis aimed at evaluating all causes that can reduce significantly the performance of the generator： in fact, building should allow to exploit increased wind intensity, but often this advantage is voided by turbulence phenomena, as in the case under investigation where the measured aerogenerator efficiency is lower than the nominal performance curve. Then, the best site can be found by crossing the contours of wind velocity with the turbulence intensity fields： in this way it is possible to localize an area （best location） where the aerogenerator can give maximum performance.

Martian ionogram scaling by the Object Tracking Method

The Mars Advanced Radar for Subsurface and Ionosphere Sounding(MARSIS) onboard the Mars Express(MEX) spacecraft started to collect data of the Martian topside ionosphere from May,2005.By now a large amount of ionograms has been obtained.It is important to extract vertical ionospheric information effectively from the ionograms for further study.In this paper a new method,Object Tracking Method(OTM),is proposed to automatically extract the ionospheric electron density profiles by computer.This method is based on three algorithms,namely the Hough transform,region growing segmentation algorithm and moving objects detection method from video sequences.In processing ionosphere echoes are treated as moving objects.The identification ratio of OTM for the MARSIS ionograms is estimated to be around 90%.

Transient stability probability of a power system incorporating a wind farm

An analytical approach for probabilistic evaluation of transient stability of a power system incorporating a wind farm is presented in this study. Based on the fact that the boundary of practical dynamic security region(PDSR) of a power system with double fed induction generators(DFIG) can be approximated by one or few hyper-planes in nodal power injection space, transient stability criterion for given configurations of pre-fault, fault-on and post-fault of a power system is to be expressed by certain expressions of linear combination of nodal injection vector and the transient stability probability(TSP) is further obtained with a much more simplified expression than the complex integral. Furthermore, considering uncertainties of nodal injection power including wind power and load, TSP is calculated analytically by Cornish-Fisher expansion, which can provide reliable evaluation results with high accuracy and much less computing time compared with Monte Carlo simulation. TSP and its visualization can further help operators and planners be aware of the degree of stability or instability and find critical components to monitor and reinforce. Test results on the New England 10-generators and 39-buses power system show the method's effectiveness and significance for probabilistic security assessment.