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     

Investigation and Simulation of Fields in Large Salient-Pole Synchronous Machines With Skewed Stator Slots

This paper presents the results of an investigative study performed on a large salient-pole synchronous machine with skewed stator slots. The study was carried out to aid the understanding of the phenomena related to electromagnetic field distribution, rotor damper currents and pole face iron losses in machines with skewed stator slots and an armature winding design with a fractional number of stator slots per pole. A hydrogenerator was specially instrumented to measure the variation of magnetic fields along the axial length of the machine and the induced currents in the damper bars on the rotor poles. A computational model has been developed to predict the air-gap flux density, damper currents and rotor iron losses. Measured results are compared with those predicted by simulation.     

Determination of damper winding and rotor iron currents inconvertor- and line-fed synchronous machines

The damper winding currents of a synchronous machine with a solid iron rotor are analyzed. Based on the self and mutual inductance modelling technique, the damper currents are described by a detailed damper model taking the damper cage and the rotor iron into account. The model's component elements are determined by the finite element method. Theoretical results are verified by measuring damper bar currents of a six-phase synchronous machine fed by two six-pulse converters. For a number of different operating modes the model is used to calculate the damper current distribution of a six-phase machine     

Comprehensive salient-pole synchronous machine parametric designanalysis using time-step finite element-state space modeling techniques

This paper details the application of a time-stepping coupled finite element-state space (CFE-SS) model to predict a salient-pole synchronous generator's parameters and performance, including damper bar current profiles and bar losses as well as iron core (including pole face) losses, under various operating conditions. The CFE-SS modeling environment is based on the natural ABC flux linkage frame of reference, which is coupled to a time/rotor stepping FE magnetic field and machine winding inductance profile computation model. This allows one to rigorously include the synergism between the space harmonics generated by magnetic saturation and machine magnetic circuit as well as winding layout topologies, and the time harmonics generated by the nonsinusoidal phase currents, ripple rich field excitation and damper bar currents. The impact of such synergism between these space and time harmonics on damper bar current profiles and losses, iron core losses, various machine winding current, voltage and torque profiles/waveforms is studied here for a 10-pole, 44.9 kVA, 17,143 RPM, 1428.6 Hz, 82 V (L-N), wound-pole aircraft generator     

变阻值Crowbar电路及其在提高双馈式风电机组低电压穿越能力中的应用

双馈风力发电机的低电压穿越能力较差,Crowbar技术是提高双馈风力发电机低电压穿越能力的有效手段。分析了DFIG机端短路时Crowbar阻值对转子电流和暂态过程的影响,指出传统Crowbar电路采用固定的阻值,无法兼顾低电压穿越过程中各阶段对该阻值的不同要求。为此提出了一种变阻值Crowbar的电路,采用这种电路只要控制脉宽就可以改变Crowbar电路的等效电阻,在电网发生地电压故障后,可以根据保护过程不同阶段的特点及时调整Crowbar电路电阻,提高双馈风力发电机的低电压穿越能力。为了验证调整效果对新设计的Crowbar电路的调整效果进行了仿真。仿真结果表明,变阻值Crowbar能够通过控制脉宽实现对Crowbar等效电阻的有效控制。     

Simulation Studies of the Transients of Squirrel-Cage Induction Motors

A new simulation approach is proposed in consideration of a saturation and a deep bar effect for the study of transients of three-phase squirrel-cage type induction motors. The mathematical model of an induction motor is expressed by the six differential equations of three-phase instantaneous voltage and current. The torque of an electric equation is related to the motion equations of motor and driven machine in the mathematical model. The values of reactance of stator and rotor are changed by the saturation of core caused by starting current. Also both the values of reactance and resistance of rotor bar are varied by the deep bar effect in the rotor core during starting. The calculation method of circuit constant that adds the influence of saturation and deep bar effect is proposed in this paper. The circuit constant of simulation model in consideration of saturation and the deep bar effect are decided by these computation methods in accordance with the conditions of rotation speed and current. If the large current flows, the leakage reactance of the stator and the rotor decreases by saturation. Moreover, the resistance of the rotor gradually decreases when the rotational speed rises from stop to synchronous speed, and the leakage reactance increases gradually. The calculated values were compared with the observed values of the examination machine of 1100 kW4P and an excellent agreement was obtained demonstrating the accuracy of the proposed simulation. Consequently, it is shown that the saturation and the deep bar effect are the essential factors to perform the accurate simulations of the induction motor. After checking the validity of the proposed approach, the simulation of the grounding faults was performed. In this study, all the simulation programs have been developed in the Matlab/Simulink environment.     

An efficient and accurate model for the simulation and analysis ofsynchronous machine/converter systems

A new synchronous machine model is presented which is readily implemented in either circuit-based or differential-equation-based simulation programs. This model is well suited for the simulation and analysis of synchronous machine-power converter systems. It is based upon standard representations and no approximations are made in its derivation. However, the numerical implementation is shown to be significantly more efficient. An example is provided which demonstrates a 1700% increase in simulation speed with no observable loss in accuracy. The model includes provisions for an arbitrary number of damper or rotor windings and may be easily modified to represent synchronous or induction machines with an arbitrary number of stator phases     

用于排架结构的铅剪切阻尼器试验及数值分析

为进一步促进铅阻尼器在工程中的应用,针对常见的排架结构,研制了一种铅剪切阻尼器,通过低周往复加载试验,逐个分析阻尼材料铅的有效剪切面积、受剪区厚度、剪切截面形式、加载位移幅值、加载频率、加载次数等因素对阻尼器耗能性能的影响。试验结果表明,设计的阻尼器的阻尼力—位移滞回曲线饱满,耗能性能良好,符合双线性力学模型,并对试验中两个典型型号的阻尼器进行了数值模拟分析,通过对比数模值和试验值,证明了数值计算模型的实用性,为阻尼器在结构体系中的减震应用奠定了基础。     

A generalized technique for modeling switch-controlled inductionmachine circuits

The main objective is to develop a generalized switch-controlled induction machine circuit modeling technique which is suitable for any switching circuit configuration. The authors present a generalized algorithm which provides a systematic procedure in connecting the formulated induction machine and the switching circuit models through the tensor approach. The formulations of the machine systems for both the switching circuits connected in the stator and rotor sides of the induction machines are derived. By proper selection of the dq reference frame, which depends on the side of the switching circuit connected to the machine, the proposed algorithm will supply an efficient and compact model suitable for arbitrary switching circuit configurations for the induction machine system. Numerical examples on the dynamic simulation of a stator-phase-controlled induction machine circuit are provided to demonstrate the validity of the algorithm     

Analysis of the steady state characteristics of doubly fedsynchronous machines

A theoretical and experimental analysis of the steady-state characteristics of a doubly fed synchronous machine (DFSM) is presented. The basic equations and the equivalent circuit that represent the steady state of the DFSM are derived. In the experiments, a three-phase symmetrical wound-rotor terminals were connected to the three-phase bus, and the rotor terminals were connected to the slip-frequency source. A DC generator was directly connected to the DFSM as a load. An AC generator driven directly by a DC motor was used as the slip-frequency source. The theoretical results were confirmed. The rotor iron loss remains an important factor, but its effect is shown to be small when slip is small     

Methodology development for estimation of armature circuit andfield winding parameters of large utility generators

This paper presents a methodology to estimate armature circuit and field winding parameters of large utility generators using the synthetic data obtained by the machine natural abc frame of reference simulation. First, a one-machine infinite bus system including the machine and its excitation system is simulated in abc frame of reference by using parameters provided by the machine manufacturer. A proper data set required for estimation is collected by perturbing the field side of the machine in small amounts, The recursive maximum likelihood (RML) estimation technique is employed for the identification of armature circuit parameters. Subsequently, based on the estimates of armature circuit parameters, the field winding and some damper parameters are estimated using an output error estimation (OEM) technique. For each estimation case, the estimation performance is also validated with noise corrupted measurements. Even in case of remarkable noise corruption, the agreement between estimated and actual parameters is quite satisfactory     

Comparison of losses and heating in generator rotors followingsevere supply system disturbances

Losses and heating in rotors of large synchronous generators are examined following sustained stator-terminal and HV busbar line-to-line short-circuits at full load and no load, three-phase (L-L-L) short-circuits on a weak line connected to the HV generator transformer busbar with clearance at fault current zeros where the generator either remains in synchronism or falls from synchronism, and worst-case malsynchronization. Comparisons are made with negative sequence losses in solid generator rotors following these disturbances. The analysis uses a phase-variable model of a synchronous generator with detailed and reduced damper representations to compute stator and rotor current following a severe electrical disturbance at either the machine terminals or the HV unit transformer busbar. Simulations at full load and no load for a variety of assumptions and approximations, with connection of a field discharge resistor on tripping the main generator breaker, are performed     

Analysis of a single-phase induction machine with a shiftedauxiliary winding

This paper extents the method of multiple reference frames to the analysis of asymmetrical induction motors with nonorthogonal stator windings, with particular emphasis on the permanent split capacitor (PSC) machine. The predictions of the method are verified by comparison to both experimental results and to results obtained using a machine variable computer simulation. Once verified, the method is used to derive the transfer function relating rotor speed to load torque disturbance, which is of particular interest when analyzing PSC machines driving compressor loads. It is shown that the transfer function exhibits a distinct resonant point, and that the magnitude of the resonant peak increases as the motor approaches synchronous speed. It is also shown that the magnitude of the resonant peak may be lowered by increasing rotational inertia or rotor resistance     

Effect of Load and Damper Modelling on Evaluation of Negative Sequence Capability of Large Generators

The paper examines negative sequence losses in solid generator rotors following sustained stator-terminal and HV system L-L short-circuits at full-load and no load with or without a connection to the grid supply. Components of stator current which give rise to rotor heating over the period of the transient are identified and effective intrinsic values ot I22 t for a range of system and machine parameters are discussed. The analysis uses a phase-variable model of a synchronous-generator with detailed and reduced damper representations to compute stator current following rated-voltage line-to-line disturbances on the supply. Simulations from full-load for a variety of system parameters with and without connection of a field discharge resistor on tripping of the generator breaker are performed. From the responses, components of stator current which give rise to rotor heating are isolated by Fourier analysis combined with symmetrical component analysis. These components are integrated over the period of the transient to give effective values of I22 t. Maximum supply-frequency components of stator current taking into account d.c. components have been assumed. Effective values of I22 t using detailed and reduced damper models in simulations with and without voltage regulator action are compared with values predicted by simpler calculations where no allowance is made for generator load or for the connection to the grid supply. A 500 MW, 3600 rpm and a 660 MW, 3000 rpm Machine are analysed.     

湿法脱硫旁路烟道流场分析

随着烟气脱硫(FGD)在我国火电机组的广泛应用,有关FGD系统对机组正常运行的影响,FGD系统以及安装FGD系统后整个电厂的安全经济运行的研究正日益提上日程。从一些电厂旁路烟道或未装挡板,或装了挡板也常开运行这一现象出发,用计算流体力学(CFD)方法分析了取消挡板前后烟道的流场特征。进行了在挡板开启/关闭的情况下,调节增压风机参数的数值实验;给出了在变负荷情况下,挡板开启的增压风机调节曲线,以达到环保、安全和经济多方面的要求;通过对温度场的考察,发现了安装温度测点的最佳位置,从温度的变化,可以反映烟气的流动情况,避免脱硫效率降低或能耗增加。     

Power quality analysis of wind farm connected to Alaçatı substation in Turkey

This paper presents simulation results and power quality measurements of a wind farm. The wound rotor induction generator at 600 kW is employed for power conversion in the wind energy conversion system (WECS). This induction machine is connected to the drive circuit via rotor terminals and speed control is carried out by means of chopper circuit. The model used in the package program is experimentally tested on the single machine drive system at 3.5 kW in the laboratory, after which the power quality issues of the wind farm are investigated by using the same model for 12 wind turbines in PSCAD.     

Micromachine for real-time generator simulation design limits and anovel solution with adjustable parameters

The authors give limits on dimensional scaling in assessing the same transient and steady-state performance of the down-scaled micromachine as that of the full-size machine. This system has the ability to model various types of synchronous and asynchronous machines in real time by means of one machine and to simulate the effects of various types of field and damper windings in the rotor without having a damper cage in the physical model of the machine. By means of this system, new types of machine control such as two-axes control and supplementary damping control can be studied. Test and identification results are given which compare favorably with a chosen set of characteristic time constants     

Effect of excitation capacitors on transient performance ofreluctance generators

The transient responses of a reluctance generator connected to an infinite power system excited by a bank of terminal capacitances are compared to those when load excitation is used. A mathematical model is developed to simulate the machine with its terminal capacitor. With the aid of a least-square-error method, this model is used to optimize the machine parameters. The capacitance excitation requirements for different load conditions are then computed using a steady-state model. The comparison of the transient responses shows that the terminal-capacitor excitation method has several advantages over the load excitation method. It reduces the first rotor swing and gives more damping to the subsequent rotor oscillations. It also increases the critical fault-clearing time and hence the transient stability limits. In addition, it suppresses all power frequency torque oscillations, which are quite pronounced when load excitation is used     

Detection of rotor slot and other eccentricity related harmonics ina three phase induction motor with different rotor cages

Detection of rotor slot and other eccentricity related harmonics in the line current of a three phase induction motor is important both from the viewpoint of sensorless speed estimation as well as eccentricity related fault detection. However, it is now clear that not all three phase induction motors are capable of generating such harmonics in the line current. Recent research has shown that the presence of these harmonics is primarily dependent on the number of rotor slots and the number of fundamental pole pairs of the machine. While the number of fundamental pole pairs of a three phase induction motor usually is within one to four (higher pole pairs are generally avoided due to increased magnetizing current), the number of rotor slots can vary widely. The present paper investigates this phenomenon further and obtains a hitherto nebulous theoretical basis for the experimentally verified results. Detailed coupled magnetic circuit simulation results are presented for a four pole, three phase induction motor with 44, 43, and 42 rotor slots under healthy, static, dynamic and mixed eccentricity conditions. The simulation is flexible enough to accommodate other pole numbers also. These simulations are helpful in quantifying the predicted harmonics under different combinations of load, pole pair numbers, rotor slots and eccentricity conditions, thus making the problem easier for drive designers or diagnostic tools' developers. Data from three different induction machines, namely, a 4 pole, 44 bar, 3 hp, a 4 pole, 28 bar, 3 hp and a 2 pole, 39 bar, 100 hp motor have been used to verify the results experimentally. The simulation and the experimental results clearly validate the theoretical findings put forward in this paper     

Effect of Damper Modelling and the Fault Clearing Process on Response Torque and Stressing of Turbine-Generator Shafts

The paper discusses the effect damper circuit modelling and the current interruption process following clearance of grid network disturbances has on machine transient response. Parameters for a 2-direct-axis and 3-quadrature-axis damper circuit model are given, as are those for lower-order damper model equivalents. Torques obtained following clearance of typical L-L-L and L-L non-ground system disturbances at fault current zeros or by simultaneous interruption for detailed and reduced damper models are illustrated. Further, the effect damper circuit modelling has on peak torque response following clearance of supply network disturbances at fault current zeros, sustained L-L-L and L-L stator terminals short-circuits and worst-case malsynchronisation is depicted.