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。     

Airflow and thermal conductance in a totally enclosed induction motor

Heat transfer coefficients of air‐cooled fins located on the outer surface of a totally enclosed induction motor were measured. It was found that the heat transfer coefficient decreases in the downstream direction in relation to the outer fins. It was also found that increasing the axial length of the fan cover (i.e., so that the fan cover overlaps the fin) increases the average heat transfer coefficient of the outer fins. Internal airflow induced by the rotor fan inside the motor end‐bracket coincides with the rotational speed of the rotor fan. Airflow velocity between the stator coil end and the housing in the motor is low, so a cooling structure with an inside ventilation passage for airflow was introduced to increase the heat transfer of the stator coil. By using an actual motor, the effect of resin (varnish) between the stator and the motor housing on the thermal‐contact conductance was determined; the thermal‐contact conductance of a motor with resin was 1.58 times higher than that of one without resin. © 2001 Scripta Technica, Heat Trans Asian Res, 31(1): 7–20, 2002     

Numerical modeling of heat transfer and fluid flow in rotor–stator cavities with throughflow

The present study considers the numerical modeling of the turbulent flow in a rotor–stator cavity subjected to a superimposed throughflow with heat transfer. Numerical predictions based on one-point statistical modeling using a low Reynolds number second-order full stress transport closure are compared with experimental data available in the literature [E.M. Sparrow, J.L. Goldstein, Effect of rotation and coolant throughflow on the heat transfer and temperature field in an enclosure, J. Heat Transfer 98 (1976) 387–394; M. Djaoui, A. Dyment, R. Debuchy, Heat transfer in a rotor–stator system with a radial inflow, Eur. J. Mech. B – Fluids 20 (2001) 371–398; S. Poncet, M.P. Chauve, R. Schiestel, Batchelor versus Stewartson flow structures in a rotor–stator cavity with throughflow, Phys. Fluids, 17(7) (2005).]. Considering small temperature differences, density variations can be here neglected which leads to dissociate the dynamical effects from the heat transfer process. The fluid flow in an enclosed disk system with axial throughflow is well predicted compared to the velocity measurements performed at IRPHE [S. Poncet, M.P. Chauve, R. Schiestel, Batchelor versus Stewartson flow structures in a rotor–stator cavity with throughflow, Phys. Fluids, 17(7) (2005)] under isothermal conditions. When the shroud is heated, the effects of rotation and coolant outward throughflow on the heat transfer have been investigated and the numerical results are found to be in good agreement with the data of Sparrow and Goldstein [E.M. Sparrow, J.L. Goldstein, Effect of rotation and coolant throughflow on the heat transfer and temperature field in an enclosure, J. Heat Transfer 98 (1976) 387–394]. Their results have been extended for a wide range of the Prandtl number. We have also considered the case of an open rotor–stator cavity with a radial inward throughflow with heat transfer along the stator, which corresponds to the experiment of Djaoui et al. [M. Djaoui, A. Dyment, R. Debuchy, Heat transfer in a rotor–stator system with a radial inflow, Eur. J. Mech. B – Fluids 20 (2001) 371–398]. Our results have been compared to both their temperature measurements and their asymptotic model with a close agreement between the different approaches, showing the efficiency of the second order modeling. An empirical correlation law is given to predict the averaged Nusselt number depending on the Reynolds and Prandtl numbers and on the coolant flowrate.     

Comparison of a CFD Analysis and a Thermal Equivalent Circuit Model of a TEFC Induction Machine With Measurements

For a totally enclosed fan-cooled induction machine, two methods of numerical analysis are compared with measurements. The first numerical method is based on computational fluid dynamics (CFDs) and the second one uses a thermal equivalent circuit (TEC). For the analysis based on CFD, a 3-D induction machine including housing is modeled. The numeric solution of the flow equations is determined for stationary temperature distributions. For the TEC, a discretized one-and-a-half-dimensional model of the induction machine is considered. With the TEC model, stationary and transient operating conditions can be simulated. Measurement results are determined by iron–copper–nickel sensors embedded in the stator winding and the housing, as well as by an IR sensor for measuring the rotor temperature. With these measurement signals, stationary and transient operating conditions can be analyzed. For stationary operating conditions, additionally, the housing temperatures are determined by an IR camera. The investigated simulation and measurement methods reveal different local and global temperatures, and thus, only certain aspects and characteristics of the obtained temperatures can be compared. Nevertheless, certain conclusions can be drawn from comparing these aspects considering the actual restrictions of each of the applied methods.      

Currents Induced in the Inner Stator Frame of Large Turbogenerators by the End-Zone Field

A method is described, based on 3-dimensional field calculations, for calculating the eddy-currents induced in the inner stator frame by the end-zone field; these currents are an order of magnitude greater than those caused there by yoke saturation, and their mechanism is explained through the calculation results for given alternative designs; it is based mainly on the shielding of the end-zone field. The eddy currents are limited mainly by the inductances; the effect of resistivity should be less than 15%. The design having the outer housing and inner frame electrically insulated from each other appears less satisfactory than the more usual design where the parts are electrically connected.     

Particle image velocimetry experimental and computational investigation of a blood pump

Blood pumps have been adopted to treat heart failure over the past decades.A novel blood pump adopting the ro-tor with splitter blades and tandem cascade stator was developed recently.A particle image velocimetry (PIV) experiment was carried out to verify the design of the blood pump based on computational fluid dynamics (CFD) and further analyze the flow properties in the rotor and stator.The original sized pump model with an acrylic housing and an experiment loop were constructed to perform the optical measurement.The PIV testing was car-ried out at the rotational speed of 6952±50 r/min with the flow rate of 3.1 l/min and at 8186±50 r/min with 3.5 l/min,respectively.The velocity and the Reynolds shear stress distributions were investigated by PIV and CFD,and the comparisons between them will be helpful for the future blood pump design.     

Analysis of impact of grid‐connected wind power on small signal stability

The power system small signal stability analysis considering wind generation intermittence is studied comprehensively in this paper. The modelling of doubly‐fed induction generator (DFIG) involving the converters with application of stator flux‐oriented vector control strategy is addressed briefly. In order to reveal how the intermittent nature of wind power affects the operating behaviour of an existing power system, a probabilistic small signal stability analysis method based on Monte Carlo simulation technique is proposed to explore and exploit the impact of intermittent grid‐connected wind power on small signal stability. The IEEE New England test system is applied as benchmark to verify the proposed model and approach. Total 3 scenarios are elaborately designed to figure out the potential relationship between the small signal stability indices and the wind generation intermittence. Finally, some preliminary conclusions and comments were drawn based on the numerical simulation results. Copyright © 2010 John Wiley & Sons, Ltd.     

Research on the Cooling System of a 4QT Prototype Machine Used for HEV

A four-quadrant transducer (4QT) is a hybrid electric vehicle (HEV) power train concept. It can enable the internal combustion engine (ICE) to operate at optimum efficiency during all driving conditions with both torque and speed control. The thermal property is a vital problem due to its special configuration. Aiming to find the hot spot and investigate the cooling system of the 4QT, the thermal field is calculated with finite-element method (FEM). The simulation is validated by the comparisons with the experiment. The influences of the forced-air cooling, water cooling, and the distribution of the cooling channels on the cooling performance are discussed, respectively. The stator air ducts are removed, and 12 water channels evenly distributed in the housing are employed. The design principle of the cooling system is presented. The speed impacts of air flow and water flow are discussed and provide a parameter reference for choosing the forced-air cooling fan and water pump properly.     

Effect of Coils on Natural Frequencies of Stator Cores in Small Induction Motors

The electromagnetic noise of a motor is offensive to the ear. Most electromagnetic acoustic noises are generated when natural frequencies of a stator core coincide with or closely parallel frequencies of the magnetomotive forces. Therefore, to minimize such noise, an accurate estimate on natural frequencies of the stator is necessary. In this paper, the stator of a small induction motor is studied as to various factors such as the stator core shape, including a circumferential cut, and stiffness of varnished random winding in stator slots. Furthermore, the effect of coil ends on natural frequencies of the stator core is newly clarified. As a result, in the 2.2kW motor, an equivalent Young's modulus as stiffness of windings in the slots is obtained as being about 1/100th that of copper. Also, study clarifies that coupling vibration arises from the coil end and the stator core. It is found that this coupling vibration can be estimated briefly from a two free degree system.     

导叶约化中心位置对涡轮非定常气动计算的影响

针对工程上常用的基于叶片数约化的涡轮非定常计算方法,为了掌握导叶约化中心位置对于涡轮内部流动非定常计算结果的影响规律,对导叶前缘约化、导叶尾缘约化、不约化三个算例进行了非定常计算与对比分析。研究结果表明:导叶前缘约化方式对于涡轮气动性能时均值影响量级在1%以上,而导叶尾缘约化方式的影响不到前者的1/2;两种约化方式均能捕捉到导叶中的主要流动特征,但前缘约化方式导叶吸力面的吸力峰更强,导叶出口的气流角与马赫数更大;前缘约化方式转静之间的势扰动更强,导叶尾迹也更强,导叶尾缘与动叶前缘上的压力波动更强。根据研究结果,对涡轮性能与流动的影响来看,同导叶前缘约化方式相比,导叶尾缘约化方式非定常计算结果同无约化方式更接近,故若采用导叶约化进行非定常计算,应优先采用导叶尾缘约化方式。     

透平叶片弯、扭、掠联合造型规律及其气动性能研究

为研究静叶弯、扭、掠联合造型对流场结构的影响,以某高压透平首级叶片为研究对象,借助计算流体力学与正交优化方法,基于动静叶最佳匹配原则（即对于每种静叶构型,动叶都进行了相应的扭转规律变化,使得动静叶气动性能处于最佳匹配状态）,研究了静叶不同复合构型方式对流场结构的影响。结果表明：在合理的静叶弯曲规律下,静叶扭转改型对透平性能有较大影响,掠改型对透平性能影响有限;在一定的扭转规律下,对静叶进行掠改型对轮周效率的影响较小,仅后掠改型会提高透平的轮周效率;对弯扭掠静叶匹配扭动叶进行联合优化,得到的最佳透平的轮周效率为87.12%,与原始透平相比,轮周效率提高了2.09%。     

Numerical simulation of clocking effect on blade unsteady aerodynamic force in axial turbine

To give an insight into the clocking effect and its influence on the wake transportation and its interaction, the unsteady three-dimensional flow through a 1.5-stage axial low pressure turbine is simulated numerically by using a density-correction based, Reynolds-Averaged Navier-Stokes equations commercial CFD code. The 2nd stator clocking is applied over ten equal tangential positions. The results show that the harmonic blade number ratio is an important factor affecting the clocking effect. The clocking effect has very small influence on the turbine efficiency in this investigation. The difference between the maximum and minimum efficiency is about 0.1%. The maximum efficiency can be achieved when the 1st stator wake enters the 2nd stator passage near blade suction surface and its adjacent wake passes through the 2nd stator passage close to blade pressure surface. The minimum efficiency appears if the 1st stator wake impinges upon the leading edge of the 2nd stator and its adjacent wake of the 1st stator passes through the mid-channel in the 2nd stator. The wake convective transportation and the blade circulation variation due to its impingement on the subsequent blade are the main mechanism affecting the pressure variation in blade surface.     

Closure to discussion of "a systematic method for the determination of the parameters of synchronous machines from the results of frequency response tests"

A. Mariscotti comments on the original paper by A. Walton (see ibid., vol.15, no.2, p.218-23, 2000). The author points out other literature that may be of use to the survey conducted in relation to whether the algorithm presented has been tested using measurement data. The original author replies to the comments     

Influence of stator structure on electromechanical parameters of torus-type brushless DC motor

Five torus-type brushless DC motors, each with a different version of the stator core structure have been analyzed in the paper. The first one is a slotless stator core and the four others have the space between the adjacent coils of stator winding filled with the material made either of iron powder composite or laminated iron. An analysis of the motor performance is based on a three-dimensional (3-D) field motor model as well as on the circuit model of the inverter + motor set supplied from the battery. The toothed stator core versions show a significant increase of the average torque, and also an increase of torque ripple caused mainly by the rise of cogging torque. The analysis based on the simulation results is backed by measurements carried out on the prototype of slotless stator version of the motor.     

Aerodynamic analysis of a stator‐augmented linear cascade wind turbine

This study proposes to attach stator vanes to PowerWindow, a linear cascade wind turbine, to improve the flow direction in the device. By controlling the angle of attack, the stator vanes increase the acting force and decrease the undesirable force on PowerWindow blades. An analytical model using blade element momentum theory is developed for the new configuration, referred to as stator‐augmented PowerWindow. The analytical model has been verified by a computational fluid dynamic simulation. This study shows that the stator vanes are able to minimize/neutralize the undesirable axial force on PowerWindow so that the thrust coefficient decreases from 0.035 in the original model to ?0.005 in the stator‐augmented one. In addition, by increasing the acting force on the blades, the stator augmentation will simultaneously enhance the coefficient of performance by up to 10%. This study also shows that by using stator vanes to control the angle of attack, unlike in the original PowerWindow, the direction of rotation of the stator‐augmented PowerWindow will remain the same regardless of the wind direction, increasing the utility of the device in practice.     

660 MW发电机漏氢原因分析与处理对策

鸳鸯湖电厂1号发电机为QFSN6602型汽轮发电机,采用水氢氢冷却方式,正常运行时发电机内氢压高于定子冷却水压力;当定子线棒存在裂纹并发生泄露时,将会导致定子冷却水含氢量急剧升高,从而使定子冷却水进入发电机造成发电机烧损.定子冷却水箱安装氢气泄露检测仪,在线检测定子冷却水箱内氢气含量,当氢气浓度达2%时就会报警.讨论了发电机定子冷却水箱内检测仪报警后的原因分析及处理,为同类机组类似故障处理提供参考.     

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     

Experimental Study of Parameters Affecting the Nusselt Number of Generator Rotor and Stator

In this research, the parameters affecting the Nusselt number of a generator rotor and stator under varying heat transfer rate are experimentally studied. In spite of the stator having no grooves, the rotor has four large triangular grooves. The temperature and then heat transfer rate of the rotor and stator are experimentally measured in three longitudinal and two angular positions. First, the effect of axial Reynolds number and rotor rotational speed on the rotor and stator Nusselt number with constant heat transfer rate ratio is studied. The range of the axial Reynolds number and rotational speed used is from 4000 to 30,000 and from 300 to 1500 rpm, respectively. Next, the effect of stator to rotor heat transfer rate ratio on the Nusselt number at constant axial Reynolds number and rotational speed is investigated. Three experiments were conducted at three heat transfer rate ratios (3, 5, and 8), defined as the ratio of heat transfer rate of the stator to the rotor. The results show that the higher the heat transfer rate ratio, the lower is the stator mean Nusselt number and the higher the rotor mean Nusselt number.     

超临界汽轮机再热第一级叶片固粒冲蚀特性的数值分析

采用数值方法计算与分析了超临界汽轮机再热第一级的固体颗粒三维运动特性,根据固体颗粒撞击叶片的位置、速度与撞击角以及叶片材料的抗冲蚀性能综合分析了静叶与动叶的冲蚀机理及冲蚀特性,指出静叶吸力面冲蚀是从动叶反弹回来的固粒撞击所引起的。此外,还分析了动静叶轴向间距及机组负荷对反弹至静叶的颗粒数量的影响,结果表明,随着轴向间距的减小和负荷的降低,反弹回静叶的颗粒数量增加。     

A novel technique for measuring grounding capacitance and groundingfault resistance in ineffectively grounded systems

A principle for resonance measurement based on injecting a resonant frequency signal is presented in this letter. Using this principle, the grounding capacitance of lines and equipment and the grounding fault resistance can be measured on-line in ineffectively grounded systems. Based on this, Petersen-coil automatic tuning is implemented and 100% stator grounding fault protection for generator stator windings is also proposed. The prototype for Petersen coil tuning has been tested on networks for many years. The new method for generator stator grounding fault protection is verified by simulation