A new approach to determine transient generator winding and dampercurrents in case of internal and external faults and abnormal operation.III. Results

For pt.II see IEEE Winter Meeting, New Orleans, LA, 1986. A novel method for analyzing the steady-state and transient currents in the stator, rotor, and damper windings of a large generator is discussed, and the application of the method to five classes of problems of practical importance is described. These are (1) internal phase-to-phase fault in a two-circuit machine; (2) 180° out-of-phase synchronization; (3) three-phase short circuit at generator terminals; (4) clearing of a three-phase system fault; and (5) unbalanced steady-state negative phase sequence load of 6%. The authors show the individual damper bar currents and energies or electric power loadings for these cases and, for one example, the time variations of stator and damper winding currents. The investigation was conducted on a standard two-pole generator that was designed for 60 Hz operation and has a rating of 700 MW     

300MW级汽轮发电机定子单扁担就位法

以华电齐齐哈尔热电厂#1机组为例,介绍了300 MW级发电机定子采用单扁担法吊装就位的施工技术措施和就位过程,吊发电机定子用的扁担及钢丝绳等的强度计算,桥吊上卷扬机钢丝绳拉力计算,桥吊轮压校核,300MW级发电机定子吊装用单扁法与双扁担法的经济性对比,以及用单扁担法吊发电机定子的推广情况。     

Effects of toothless stator design on dynamic model parameters ofpermanent magnet generators

The effects of toothless stator design on the dynamic model parameters of permanent magnet (PM) generators are presented. These parameters, which include inductances and induced back EMFs, are determined for a 75 kVA, 208 V, 400 Hz, two-pole, permanent magnet generator. Two particular stator designs, a toothless stator, and a conventional type stator (with iron teeth), are considered. The method which is used to determine these parameters is general in nature and is based on the use of a series of magnetic field solutions. A validation of the computed EMF and inductance values based on experimentally obtained data is given. The results of using these parameters in a state space model in the abc frame of reference to study the effects of a toothless stator design on the PM generator synchronous inductances are presented. Based on that, it is demonstrated that the effects of rotor saliency and armature loading on the machine parameters are minimized in the case of the toothless design     

Peaked-MMF smooth-torque reluctance motors

The authors investigate the steady-state torque characteristics of reluctance motors with nonsalient stator punchings, but with peaked rotating magnetomotive forces (MMFs). The torque calculation includes the effects of saturation and fringing and groove fluxes. The peaked rotating MMF is produced by properly coordinated current waveforms and winding. Peaked-MMF reluctance motors have tow major advantages: the torque is smooth and the flux per pole required to produce a given torque is lower than that of conventional reluctance motors. This property is most beneficial to two-pole reluctance motors, for a given frame whose bore diameters and slot areas can be increased significantly for higher ratings or better performance. Unlike switched reluctance motors, shaft encoders are not required for peaked-MMF motors     

Theoretical development and experimental verification of a DC-ACelectronically rectified load-generator system model compatible withcommon network analysis software packages

A method for modeling electronically commutated DC-AC load-rectifier-generator systems is presented. The method is based on a modified form of Park's d-q-o transformation, and yields an equivalent system network which is compatible with most commonly known network analysis software packages. The method was used to develop a model for the simulation of the dynamic steady-state performance of a DC-AC system consisting of a 30 kVA, three-phase, 208 V, four-pole, 400 Hz generator feeding a rectifier-load system. The system was tested in the laboratory under various DC and combined DC-AC load conditions. The results of the simulation model reveal a dynamic steady-state performance of the load-rectifier-generator system, in very good agreement with the test results. The applicability of the method and model to other electronically controlled machine systems is discussed in the light of those results     

Stressing of turbine-generator-exciter shafts by variable-frequencycurrents superimposed on DC currents in asynchronous HVDC links andfollowing disturbances at converter stations

Ripple currents on the DC side of both HVDC synchronous and asynchronous links together with cleared HVDC and AC system disturbances can excite in some circumstances onerous torsional vibrations in large steam generator shafts. The problem has assumed importance in recent months on account of the HVDC link between Scotland and Northern Ireland going ahead, on account of the proposed Eire/Wales link, and because AC/DC/AC couplers are to be installed extensively to interconnect the East and West European grid systems. This paper discusses and analyses excitation of shaft torsional vibrations in steam turbine-generator-exciter shafts in close proximity to HVDC power converter substations by: (i) variable-frequency ripple currents superimposed on the DC currents in asynchronous links; and (ii) disturbances at bi-polar converter stations. Detailed simulation of the HVDC converter and generator is necessary for precise assessments of shaft torsional response following HVDC converter station faults. 500 MW, 660 MW, 1000 MW and 1300 MW machines are considered in the analyses that are made     

Test and simulation of network dynamic response using SSFR and RTDRderived synchronous machine models

The comparative testing of four 60 Hz two-pole generators indicates practical advantages for the SSFR (standstill frequency response) method over the RTDR (rotating time-domain response) method when synchronous machine models are to be synthesized from test data for network dynamic performance analysis. Manufacturer-provided data are compared to SSFR and RTDR derived parameters. All adequately duplicate synchronization, load rejection, and line switching tests. Deterministic sensitivity of CFCT (critical fault clearing time) to selected machine parameters is reported     

高均匀性稳态磁场发生装置的优化研究

  目的  为了考核电力与电子设备的抗磁场干扰能力,需要进行相应的磁场抗扰度测试,其中高均匀性稳态磁场发生装置是稳态测试装置的核心部件。  方法  以常规Helmholtz和Maxwell方形线圈为研究对象,通过数值计算进行参数优化,解析得出能够产生高性能磁场的线圈结构,并使用有限元法建立模型进行计算,验证了结果的正确性。  结果  通过数值分析得出线圈参数的一般通用计算公式,并对比两种线圈型式,选择尺寸和功耗较小的优化型Maxwell方形线圈作为最终结构。  结论  为高均匀性稳态磁场发生装置提供了详细的计算过程和设计参考,可以给电气行业的相应设备设计提供理论依据。     

1000MW等级超超临界锅炉张力板结构的强度计算及优化

张力板是锅炉螺旋管圈水冷壁的重要部件,其主要作用是通过槽型钢、张力板、手指板等一系列结构将螺旋管圈荷载传递至垂直管圈。本文利用有限元计算方法,对1000MW等级超超临界n型布置锅炉张力板及手指板结构强度进行计算分析。并根据计算结果,对该结构提出了优化方案。     

Broken rotor bar detection in induction machines with transient operating speeds

Previous work on condition monitoring of induction machines has focused on steady-state speed operation. Here, a new concept is introduced based on an analysis of transient machine currents. The technique centers around the extraction and removal of the fundamental component of the current and analyzing the residual current using wavelets. Test results of induction machines operating both as a motor and a generator shows the ability of the algorithm to detect broken rotor bars.     

Modelling and controller design of an isolated diesel enginepermanent magnet synchronous generator

A method to analyze the steady-state performance of a stand-alone permanent magnet synchronous generator driven by a diesel engine is presented. The proposed method is based on equivalent d-q circuits and the phasor diagram of such a generator under steady-state conditions. A fixed capacitor-thyristor controlled reactor scheme is used to regulate the generator terminal voltage by controlling the thyristor ignition angle. Furthermore the overall system dynamics are modelled in terms of state variables and control inputs. Based on a reduced order linearized model, digital optimal state and output feedback controllers are designed by minimising a quadratic performance index using the dynamic programming technique. The objective of the controller is to maintain the load voltage and frequency constant under varying load conditions. The controller's effectiveness is assessed by examining the closed-loop system response to sudden load changes     

Saturation Modeling and Stability Analysis of Synchronous Reluctance Generator

A new method of representing magnetic saturation in synchronous reluctance generator has been proposed in this paper. A linearized model of synchronous reluctance generator has been developed applying the proposed saturation model to perform the steady-state stability analysis. The effect of $d$ - and $q$-axis saturation on the steady-state stability of a synchronous reluctance generator has been investigated using the proposed linearized machine model. Effects of different loading conditions such as active power, reactive power, and power factor on the steady-state stability have also been looked into. Moreover, the effect of $d$- and $q$-axis saturation on the transient stability analysis has been investigated in the case of a three-phase symmetrical ground fault at the machine terminals.      

Computer modeling and parametric study of a double effect generation absorption refrigeration cycle

This paper presents as assessment based on steady-state thermodynamic analysis and computer modeling of a double effect generation absorption refrigeration cycle for solar air-conditioning. The system consists of a second effect generator between the generator and condenser of the single effect absorption cycle and two solution heat exchangers between the absorber and the two generators. A numerical computer modeling of a water LiBr system based on the solution of simultaneous heat, mass and material balance equations for various components of the system has been carried out. The influences of component temperatures and heat exchanger effectiveness on the cooling coefficients of performance and component heat transfer rates have been investigated to obtain optimum operating conditions for the proposed air-conditioning system. Further, the single and double effect absorption cycles are compared with each other as well as with an ideal absorption cycle operating over the same range of temperatures.     

Zero sequence method for energy recovery from a variable-speed windturbine generator

An innovative power conversion system to convert energy from a variable-frequency wind-powered induction generator to a fixed frequency output is presented. A standard six-switch DC link current regulated pulse width modulated (CRPWM) inverter is simultaneously modulated with two current components. A three-phase balanced current component at the induction generator's optimum operating frequency transfers energy from the generator to the converter. A single phase zero sequence current component at a fixed 60 Hz frequency transfers energy from the converter through a zero sequence filter to the load. Unity power factor output is shown both in simulation and experiment, though any arbitrary power factor output may be readily commanded. Maximum power capture for a variable-speed wind turbine is achieved using proven control techniques. This method uses only half of the active power switching devices of conventional conversion methods. Simulation and experimental verification are shown     

An analysis of bearingless AC motors

Several types of AC bearingless motors are proposed. These bearingless motors have conventional four-pole stator windings and additional two-pole windings, whose currents produce radial forces acting on the rotor. General expressions of the machine inductances and radial forces are derived for the cylindrical rotor and salient-pole motors. No-load characteristics of laboratory squirrel-cage induction and reluctance-type synchronous bearingless motors are provided. The test motors were successfully driven by the control circuits     

大型汽轮发电机壳体异常振动诊断及治理方法研究

针对大型汽轮发电机组发电机定子壳体振动超标和非稳态振动问题,提出了一种基于发电机壳体结构共振的故障识别及综合治理方法,并以某300 MW和某630 MW机组为例进行了验证。结果表明：发电机定子底部载荷分布不均诱发的连接刚度下降和发电机转子的热不平衡是导致发电机定子局部共振或振动超标的主要原因,采取载荷均布调整、现场动平衡等措施,可消除此类故障。     

汽轮发电机组轴系扭振特性计算分析

介绍了采用多段集中质量模型计算轴导振特性的两种方法：传递矩阵法及特征向量。并利用上述两方法对某电厂１号机轴系的扭振特性进行了计算分析。     

Steady-State Analysis of a Self-Excited Single-Phase Reluctance Generator

This paper presents an analytical method for predicting the steady-state performance of a self-excited single-phase reluctance generator (SESPRG), which supplies R-- L load. The proposed analysis is based on the d--q axis model and phasor diagram of such a generator in the steady-state condition. Excitation capacitors are connected across both the main and auxiliary windings. Magnetic saturation is taken into account and is assumed to be confined to the direct axis, and is accounted for a variable direct-axis magnetizing reactance. Conditions of self-excitation and the minimum value of the capacitance required to achieve self-excitation are also given. Special attention is focused on the machine performance when it operates as a pure single-phase reluctance generator (PSPRG). A fixed-capacitor (FC) thyristor-controlled reactor (TCR) scheme is used to regulate the generator terminal voltage by controlling the thyristor conduction angle. Further stability limits are investigated by developing the active-reactive (P-Q) power diagram. Reasonably close agreement between the measured and predicted results is observed confirming the validity of the proposed analysis.     

负荷波动对灯泡贯流式水轮发电机转矩及损耗的影响

针对灯泡贯流式水轮发电机组负荷波动影响发电机转矩波动及转子涡流损耗的问题,以一台24 MW灯泡贯流式水轮发电机为例,利用有限元法建立了水轮发电机二维电磁场模型,并计算了发电机负载运行与空载运行时的定子绕组的电压与电流,验证了模型正确性。在此基础上,对比分析了发电机组工作在不同负荷工况下发电机的转矩脉动系数及其转子涡流损耗的差异,并得到二者随机组负荷的变化规律,揭示了机组负荷波动对发电机转子涡流损耗的影响机理,为灯泡贯流式水轮发电机的设计提供参考。     

Improving wind turbine drivetrain bearing reliability through pre‐misalignment

Improving the reliability of wind turbines (WT) is an essential component in the bid to minimize the cost of energy, especially for offshore wind because of the difficulties associated with access for maintenance. Numerous studies have shown that WT gearbox and generator failure rates are unacceptably high, particularly given the long downtime incurred per failure. There is evidence that bearing failures of the gearbox high‐speed stage (HSS) and generator account for a significant proportion of these failures. However, the root causes of these failure data are not known, and there is therefore a need for fundamental computational studies to support the valuable ‘top down’ reliability analyses. In this paper, a real (proprietary) 2 MW geared WT was modelled to compute the gearbox–generator misalignment and predict the impact of this misalignment upon the gearbox HSS and generator bearings. At rated torque, misalignment between the gearbox and generator of 8500 µm was seen. For the 2 MW WT analysed, the computational data show that the L₁₀ fatigue lives of the gearbox HSS bearings were not significantly affected by this misalignment but that the L₁₀ fatigue lives of the generator bearings, particularly the drive‐end bearing, could be significantly reduced. It is proposed to apply a nominal offset to the generator to reduce the misalignment under operation, thereby reducing the loading on the gearbox HSS and generator bearings. The value of performing integrated system analyses has been demonstrated, and a robust methodology has been outlined. Copyright © 2013 John Wiley & Sons, Ltd.