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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
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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
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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
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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
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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
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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
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F. BENCHABANE A. TITAOUINE O. BENNIS K. YAHIA D. TAIBI A. GUETTAF 《Frontiers in Energy》2012,6(3):247
In this paper, a new sensorless interior permanent magnet synchronous motor (IPMSM) drives method with extended Kalman filter (EKF) for speed, rotor position and load torque estimation is proposed. The direct torque control (DTC) technique for permanent magnet synchronous motor (PMSM) is receiving increasing attention due to the important advantages of the low dependence on motor parameters when compared with other motor control techniques. The Kalman filter is an observer for linear and non-linear systems and is based on the stochastic intromission, in others words, noise. The PMSM is fed by an indirect power electronic converter which is controlled by a sliding mode technique. The simulation tests performed for different operating conditions have confirmed the robustness of the overall system; and it is shown that the sliding mode technique has successfully minimized the different harmonics introduced by the line converter. 相似文献
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U. A. Tadzhiev E. I. Kiseleva M. U. Tadzhiev R. A. Zakhidov 《Applied Solar Energy》2012,48(2):146-151
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
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T. Kuroki N. Sakoda K. Shinzato M. Monde Y. Takata 《International Journal of Hydrogen Energy》2018,43(5):2531-2539
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
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Guohua Ni Yan LanCheng Cheng Yuedong MengXiangke Wang 《International Journal of Hydrogen Energy》2011,36(20):12869-12876
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
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《International Journal of Hydrogen Energy》2022,47(67):29162-29171
Hydrogen is becoming more popular as a fuel for vehicles. It is stored and dispensed at hydrogen refueling stations. Once the hydrogen in hydrogen refueling stations leaks, it easily forms a combustible cloud, and can explode by encountering a spark. It is therefore important for the safe and stable operation of hydrogen refueling stations to analyze the evolution of a leakage and explosion accident, clarify the causes and processes of the accident, and prevent the spread of risks. This paper proposes a model using multi-level variable weight fuzzy Petri net. On the basis of hierarchical consideration of the development of the accident, it adds a variable weight factor, which can quantify information in the development of the accident. According to the calculated results, the evolutionary path of risk and the most likely initial cause of the accident are deduced. Finally, taking the leakage and explosion accident of an urban hydrogen refueling station as an example, the usability and effectiveness of the model are verified. 相似文献
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直流电网技术对设备提出了新的要求,具有快速开断能力的高压直流断路器是直流电网的核心设备,现有试验技术在功率方面不能满足直流断路器短时电流耐受试验的要求。为解决该问题,该文分析了在直流电网中直流断路器耐受的短时电流应力,提出了基于损耗及结温等效的试验方法及试验电路拓扑,搭建了PSCAD/EMTDC电磁暂态仿真模型。并以张北工程康宝站为例,对直流断路器短时电流耐受试验进行了仿真验证。仿真结果表明:该试验电路能够有效地实现短时电流对直流断路器的应力考核,为试验平台的设计提供指导作用。 相似文献
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《Power and Energy Magazine, IEEE》2010,8(1):80-82
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
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Modelling the effect of coating on the stresses and microstructure evolution in chill casting of wind turbine main shafts
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The purpose of the present work is to quantify the effect of the inside coating on chills for casting of large wind turbine main shafts with respect to the evolution of internal stresses. These are known to affect the lifetime of the chills, and this is a major cost for the foundries today. Simulations of the casting process are performed with four different heat transfer coefficients (HTCs) between the casting and the chill, and the resulting transient stress fields are reported in the chill. The microstructural evolution in the casting in terms of the nodule count is also modelled in the simulations. The outcome is validated by comparisons with samples taken out from a critical region of main shafts cast in sand and in chills. The results reveal minor reductions in the maximum principal stresses on the inner and outer surfaces of the chill of 3.1% and 18.5%, respectively, from changing the HTC from 2000 to 500 W m?2 K?1. These results indicate that the lifetime of the chill will not be significantly improved by adding a thicker layer of coating. The microstructure evolution is not very much affected by the HTC value with a maximum reduction in nodule count of 6.5%. Therefore, it is concluded that the material quality obtained from casting the main shafts in chills (and hence the performance of the part) is still much better than for sand casting, even though a very thick layer of coating is applied. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献