首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
The paper makes an indepth analysis of the excitation of shaft torsional vibrations in steam turbine-generator-exciter shafts by variable-frequency ripple currents superimposed on DC currents in asynchronous links using the finite element and reduced models of the machine shafts. Frequencies at which sympathetic shaft torsional vibrations would be excited by modulation product harmonics in 50 Hz/50 Hz and 50 Hz/60 Hz asynchronous links as a function of deviation in system frequency are illustrated. It is shown that amplitude of shaft torque due to steady resonant torque excitation is a function of initial rate of increase of vibrations at adjacent cells, the time constant for decay of the vibration, and stiffness between adjacent shaft cells  相似文献   

2.
Phenomena that affects the performance of transducers that measure torque at positions along a turbine-generator shaft are reviewed, and the design of a transducer for precise measurement of torque at positions on a steam turbine-generator shaft that results from severe disturbances of the electrical supply system is discussed. Torque at shaft couplings following severe supply system events predicted using continuum models of turbine-generator shafts are analyzed and compared with that obtained over a section of the shaft by shaft twist and overall stiffness of the section. Algorithms for processing torque deduced from twist over a section to estimate true torque at specific shaft locations are discussed. Studies are performed for severe L-L-L short circuits with clearance. The design of a transient shaft torque transducer which uses disks with slits which are secured to the rotating shaft is described  相似文献   

3.
The paper first summarises the advantages of steam turbine-driven induction generators over conventional generators such as low cost, less maintenance, rugged and brushless rotors (squirrel cage type, no need for synchronisation, etc.), together with problems concerning excitation (VAr compensation at loads etc). A mathematical model of the induction generator simulated in direct-phase quantities where saturation of the magnetising reactances is simulated and saturation of stator and rotor leakage reactances is ignored is developed and employed for detailed simulation of the machine. Discrete-mass models of the machine shaft where both steam and electrical viscous damping is simulated are employed in comparing transient shaft torsional response evaluated by time domain simulation and frequency domain analysis following incidence and clearance of severe system faults. The paper then investigates torsional response following incidence and clearance of severe supply system disturbances, when the rotor is stationary and when running at close to synchronous speed unexcited, and following malsynchronisation when excited by a controlled VAr source, together with torsional response following bolted stator-terminal short-circuits at full-load and no-load following switching in of the induction generator onto the system supply. It examines precision of predicting torque in turbine-generator shafts by frequency domain analysis not analyzed for induction generators in the literature heretofore following incidence and clearance of worst-case disturbances on the supply. Effect of steam and electrical damping on maximum shaft torques predicted by frequency domain analysis is also illustrated. The results illustrate there is no tendency for shaft torques to become more onerous as the fault clearing time is increased as is the case for shaft torques in large synchronous machines. Three large two-pole machines of rating of up to a few hundred MWs are analysed  相似文献   

4.
针对燃料电池输出端电压低且变化范围宽,需较高的直流电压增益才能实现并网发电的特点,文章研究了一种基于交错控制和平均电流控制的新型高增益直流变换器,该变换器不仅具有较高的电压增益、合适的占空比、脉动较小的输入输出电流纹波,开关管承受的电压电流应力远远低于传统的二次型Boost变换器,而且控制电路简单等特点。文章详细分析了该变换器的工作原理、稳态性能,并对其进行了小信号的建模分析,通过仿真验证了所研究的拓扑电路和控制方法的可行性。  相似文献   

5.
田庆 《水电能源科学》2011,29(12):147-150
针对天广直流控制保护系统改造完成后发生的3次双极线路保护动作事故,剖析了直流线路突变量保护误动的原因,并基于天生桥换流站和广州换流站的实际录波和过程,结合突变量保护定值和整定原则,分析了导致突变量保护误动的影响因素,提出了防范措施和建议.实例验证结果表明,该措施行之有效,为直流控制保护系统国产化改造提供了参考.  相似文献   

6.
介绍了南汇柔性直流输电系统的直流接地电阻、安装位置、电气参数及相应作用.通过排查隐患,分析了自2011年7月25日投运以来柔性直流输电系统出现的直流接地电阻问题.针对直流接地电阻设备的固有缺陷做了技术分析.尤其是对直流接地电阻的日常巡视、定期保养维护等问题,提出了治理措施和整改建议,为柔性直流输电技术的推广应用,提供技术支撑和运行经验.  相似文献   

7.
This paper analyzes rectifier ripple current superimposed on the direct current of a 600 MW asynchronous bipolar link between Lithuania and Poland and a 600 MW asynchronous monopolar link between Poland and Sweden in evaluating possible torsional vibrations in steam turbine-generator-exciter shafts. The studies are performed for machines in Northeastern Poland and in Southern Sweden close to the inverter station which are most at risk. Analyses are performed for the generators in Poland for the Lithuania/Poland link and for the generators in Sweden for the Poland/Sweden link. The paper examines system scaling factors for the Lithuania/Poland Link. It then examines AC system scaling factors and generator scaling factors for modulation product harmonic currents impressed on generators connected to the Swedish Grid Network by the inverter. Amplitude of shaft torsional torque due to resonant excitation imposed by the link on the generators in Sweden is evaluated for different scenarios of system and generator load. First, theory which relates magnitude of harmonic AC current injected into the AC system by the inverter is summarized. Dispersion of the injected harmonic AC current to proportion the current to individual generators is then reviewed, considering impedance of the generators, loads, and other system elements. Significance of simple and detailed shaft train models of machine shafts as well as approximate (Id, Iq) and detailed (2d, 3q) generator damper models on resonant torques is reviewed. Then, effects of both power factor and generator load on generator scaling factors is illustrated  相似文献   

8.
The study of harmonic instabilities in an AC/DC power system is presented in this letter. An existing frequency domain methodology is modified to assess the phenomena produced by this harmonic interaction. A set of analytical equations is derived to compute the commutation time taking place in the single-phase converter. Suitable guidelines are suggested for effective overlap angle initializations. Test results are presented that demonstrate the effectiveness of the proposed methodology. Instabilities are shown to take place for given operating conditions  相似文献   

9.
We demonstrated the possibility of improving the energy efficiency of hydropower stations at irrigation reservoirs based on the energy use of mountain-valley wind flows of surface layers of the atmosphere through the establishment of wind power generation superstructures to the hydroelectric power station that work with them.  相似文献   

10.
由我国风力资源的分布特点所决定,很多双馈风电机组都建在一些电网比较薄弱的偏远地区,这些地区经常发生电网电压和电流不对称的情况。如果在控制中对该情况不予考虑,会引起直流母线电压波动和纹波电流。三相电压和电流的不平衡可以从正序和负序分量中得到体现。文章基于三相三序变换理论,结合RC相移电路,提出了一种硬件电路来进行三相电压和电流的正序和负序的检测,通过仿真以及在实际控制策略中的应用,证明了该电路的正确性和有效性。  相似文献   

11.
This study focuses on two types of hydrogen-gasoline hybrid refueling stations, and a risk assessment study on thermal radiation is carried out with a fire at each hybrid station. One of the hybrid stations has bare hydrogen storage cylinders, and the other has container walls around the cylinders. We calculate radiative flux to the cylinders from the fire occurring at the gasoline refueling machines in each hybrid station. Additionally, we calculate the temperature rise of the cylinders based on the obtained radiative flux. To evaluate a dangerous case for hybrid stations, we calculate the radiative flux and temperature rise using a large scale and high temperature fire. Based on our analysis, we find that the container walls can greatly insulate the radiative flux. Therefore, we show that we are able to keep the temperature of the cylinders below the hazardous temperature of 358 K by installing container walls around them.  相似文献   

12.
An experimental plasma chemical reactor, equipped with a novel water plasma torch, was used for reforming methane and carbon dioxide mixture to produce synthesis gas (syngas). Water plasma is generated by the torch at atmospheric pressure, in the absence of carrier gases, water cooling system and special steam supply system. The influence of the ratio of CO2 to CH4 and total feed gas rate on syngas production, composition and energy conversion efficiency were investigated. Compared to other plasma technologies, the higher reaction performance was obtained by the novel water plasma process. The results show that, under optimum experimental conditions, the energy conversion efficiency reaches up to maximum value of 1.87 mmol/kJ and the highest energy efficiency of 74.63% is achieved, which is higher than that of other plasma processes. Furthermore, the obtained syngas with high mole ratio of H2 to CO (close to 2) is suitable for the direct industrial application.  相似文献   

13.
在剖析风力发电励磁系统中矩阵式变换器空间矢量调制算法基本原理的基础上,指出传统的直接反正切算法在扇区划分及扇区角判定中存在两大缺陷,揭示了该缺陷形成的根本原因。针对该算法在用DSP等处理器进行算法实现中存在扇区划分及扇区角判定数据处理量大、精度低、编程实现复杂等缺点,提出了二倍角反正切算法,论述了该算法的基本原理,并通过构建SIMULINK仿真模型对两种算法进行了对比分析。结果表明,二倍角反正切算法编程实现简单、系统数据处理量减少50%。  相似文献   

14.
This book succeeds in providing a comprehensive textbook on HVDC system design, planning, and application issues. A wide range of subjects including power electronics, power systems, substation design, and control system design are covered. A second edition of the book could benefit from an increased number of references, the quotation of the references in the body text, the provision of time-domain plots for power system integration performance of the HVDC, and the inclusion of a more detailed discussion on power system integration performance of VSC HVDC.  相似文献   

15.
A mathematical model for the development of a segregated layer of exudated droplets during DC casting of aluminum ingots is established. The model accounts for the metallostatic pressure driven interdendritic melt flow through the mushy zone by a Darcy type equation, the surface segregation due to this melt flow, and the decrease of the total solute concentration in different positions of the mush as a result of the exudation. The solution domain for the governing differential equations is constituted by the mushy zone of the cast. The main physical phenomena included in the model have been studied in a simple one dimensional case study.  相似文献   

16.
李立新 《江西能源》2004,(2):25-26,39
针对企业通信专网用24V直流电源的现状,提出改造方案,并对多种方案进行比较,选择最优方案实施。  相似文献   

17.
为考察外加直流电场作用对微生物燃料电池阳极微生物的影响,采用双室型MFC反应器,在启动开始时分别加以-5,-3,-1,0,+1,+3,+5 V的直流电场,作用时间依次取2 min,30 min,1 h,24 h。结果表明,外加直流电场能够对微生物燃料电池阳极室内微生物的生长产生影响,作用时间为30 min时效果较为明显,提高作用时间后效果变化不大;±1 V的电场强度作用促进微生物的生长;较低的直流电场(±1 V)作用能够促进微生物燃料电池的阳极生物挂膜,且负电场促进效果更好,而较高的直流电场(+3 V和±5 V)作用不利于甚至损害阳极生物挂膜。  相似文献   

18.
19.
中小型水电站技术改造是水电事业发展的重要组成部分 ,本文通过对我国中小型水电站发展现状的论述 ,分析了在中小型水电站技术改造中水轮机转轮改型设计的必要性和可行性 ,并介绍了当前水轮机转轮设计、测试和制造方面的新技术。  相似文献   

20.
崔峰  李志晓  刘捷  巩超 《节能》2009,28(2):38-40
针对山东中烟工业公司济南卷烟厂空压机变频器工作时产生的谐波电流导致厂内动力部分出现变压器温度过高、噪音增大、信号波动、通讯中断等故障现象,采用并联型有源电力滤波器进行谐波治理。对并联型有源电力滤波器的控制系统和主电路进行了介绍,给出现场谐波治理的方案。通过该滤波器现场运行效果表明,并联型有源电力滤波器具有理想的谐波补偿效果,同时降低了空压机运行的电流,实现节能降耗。  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号