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     

Identification of armature, field, and saturated parameters of alarge steam turbine-generator from operating data

This paper presents a step by step identification procedure of armature, field and saturated parameters of a large steam turbine-generator from real time operating data. First, data from a small excitation disturbance is utilized to estimate armature circuit parameters of the machine. Subsequently, for each set of steady state operating data, saturable mutual inductances L_ads and L_aqs are estimated. The recursive maximum likelihood estimation technique is employed for identification in these first two stages. An artificial neural network (ANN) based estimator is used to model these saturated inductances based on the generator operating conditions. Finally, using the estimates of the armature circuit parameters, the field winding and some damper winding parameters are estimated using an output error method (OEM) of estimation. The developed models are validated with measurements not used in the training of ANN and with large disturbance responses     

Lumped modelling of open-circuit turbogenerator operationalparameters

Solid-rotor turbine-generators have commonly been derived from the fitting of curves to terminal characteristics obtained by measurement or from finite element simulations. The paper presents a new method to represent the open-circuit operational inductances of a large turbogenerator of 150 MVA. The method differs from current estimation techniques because the lumped model and its parameters are determined simultaneously. It is based on a finite-element electromagnetic linear analysis of the solid-rotor machine cross section in the frequency domain. Network theory is used to characterise the quadrature-axis model where the problems of model structure and parameter determination are treated. A q-axis equivalent circuit with one damper winding and frequency dependent parameters is found. In addition, an analysis of the machine d-axis is presented. It is based in an electromagnetic study of the “black box” two-port network, where the open-circuit operational inductances are represented by frequency dependent parameters     

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     

Transient state analysis of a doubly-fed induction generator underthree phase short circuit

The doubly fed induction generator (DFG) is a variable-speed constant-frequency generator operating in either subsynchronous or supersynchronous mode. The transient behavior of a symmetrically loaded DFG after a three-phase short circuit is presented. Both speed and rotor excitation voltage and frequency remain unchanged during short circuit. The complete mathematical model of the transient state and experimental results are given, along with the transient state equivalent circuit     

双馈感应风力发电机的负电阻效应研究

为评估双馈风电场经串补送出系统的振荡风险,该文重点对双馈风力发电机的负电阻效应进行研究.首先,结合双馈风力发电机常用的控制结构,通过分析其扰动响应特性建立端口导纳模型.在此基础上,通过等效电路分析建立异步发电机转子回路的等效阻抗模型.进一步地,对转子回路的负电阻特性进行研究,并定义2个特征指标来定性评估系统的振荡风险....     

双层叠绕组发电机单元件横差保护特性分析

通过1号机横差保护动作的现象,对故障进行分析,得出测量双星形中性点电流作为双层叠绕组发电机单元件横差保护的,横差动作的原因可能是定子绕组匝间发生短路,也可能是转子匝间短路或者转子偏心引起磁场不均匀也会引起的结论,该结论对现场维护人员有一定得指导意义。     

Rotor design of a 1000 MW superconducting generator

A conceptual rotor design was developed for a 1000 MW superconducting generator having a high-initial-response excitation system. Field winding design, magnetic field analysis of the field winding, and loss calculations and force and stress analyses for the rotor body were carried out. The results are as follows: (1) the operating point of the field winding at the transient state is 72% of the short sample characteristics; (3) the stress in the rotor teeth at the steady state is 405 Pa; and (4) high initial response excitation can cause quenching of the field winding, so the shaft should have a higher resistivity. The maximum flux density at the field winding end region can be small due to optimum magnetometer force distribution     

Coupled finite-element/state-space modeling of turbogenerators inthe abc frame of reference-the no-load case

This first of two companion papers centers on applying a coupled finite-element/state-space technique to the determination of self and mutual winding inductances of a 733 MVA turbogenerator and computing its open-circuit characteristic, in the natural abc frame of reference. In this method, the apparent self and mutual inductance profiles of the armature and field windings, expressed as functions of rotor position angle, are computed from a series of magnetic field solutions performed at uniformly-distributed samples of rotor positions covering the entire 360° electrical cycle, using the energy perturbation method. These inductances, which are obtained at no-load for three different excitation levels, include the full effect of space harmonics introduced by the magnetic circuit geometry, winding layouts and magnetic circuit saturation. The abc-frame/finite-element computed open-circuit characteristic is in excellent agreement with the test results. This computed no-load set of parameters forms the initial data for simulation of the full-load performance given in the companion paper, including the full impact of space harmonics and saturation on the flux linkage, current and voltage waveforms, and other performance parameters     

Simulation of Partial Discharge Propagation in Power Network

Locating partial discharge (PD) using single-pulse analysis is considered in this research. The studied network is a generator connected to a transformer through the busbar. Since the stator winding of a generator consists of a finite number of wound coils and finite length busbar, an analysis based on a simple ladder transmission-line model with a finite number of sections has been carried out. A simulation study using the SIMULINK package on the model produces network frequency responses under varied line parameters, and a varied number of sections and termination conditions. The investigation shows that the results of simultaneous PD measurements at different locations can be reproduced satisfactorily using the network model in terms of predicting its resonant frequencies and the time-domain envelope profile of the PD. The proposed method enables one to discriminate PD pulses originating from different locations of the generator winding, as it is observed that the PD magnitude attenuates during propagation.     

Analysis and Detection of Short Circuits in Fractional Horsepower Commutator Machines

An improved mathematical model for transient simulations of commutator machines is presented in this paper. This model can simulate and predict the line current harmonics during healthy and faulty operation conditions. A lumped parameter model that considers every single coil in the stator and rotor as a separate electrical and magnetic circuit is proposed. Self and mutual inductances of the coils are estimated by means of the winding function approach (WFA), accounting for the most relevant space harmonics in the machine air gap. The commutation is modeled by using the real brush width and assuming that the brush-commutator contact resistance is a function uniquely of their contact area, which depends on the armature position. Short circuits between adjacent commutator bars are investigated. It is shown that the model achieves good accuracy, reproducing fairly well the armature current ripple for healthy and faulty operation of the machine.     

Voltage-frequency control of a self-excited induction generator

A new strategy for controlling voltage and frequency of a self excited induction generator (SEIG) is presented. The SEIG operates in the linear region of the core magnetizing curve, so that efficiency and performance are upgraded. An external excitation circuit, comprising permanently connected capacitors and electronically switched inductances is used. The external circuit allows to compensate for the generator reactive demand. A detailed analysis is performed, showing some salient aspects related to the connection of the external excitation circuit on the control performance. Asynchronous switching is used, but some important considerations must be taken into account related to the instantaneous phase angle between stator voltage and external inductor current at the switching instant, if good transient response is desired. Sliding mode controllers are proposed, showing good dynamic response and robust behavior upon changes in load and generator parameters. Computer simulations are used to demonstrate the validity of the proposed scheme     

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     

Hybrid-State-Model-Based Time-Domain Identification of Synchronous Machine Parameters From Saturated Load Rejection Test Records

This paper presents a suitable method for time-domain identification of synchronous machine parameters from the hybrid state model recently introduced by the authors in a compact matrix form. The saturated version of this model is developed in terms of generator equivalent-circuit parameters. The load rejection test of a combined resistive/inductive load is performed for the parameter identification while the online symmetrical three-phase short-circuit test is carried out for the model cross-validation. For weak power factor initial loads connected to the generator, the rotor speed is quite constant during the full load rejection test. Thus, the mechanical transients do not have any influence on estimated electrical parameters since they are decoupled from the electrical model of the machine. The method is successfully applied for the parameter identification of 380 V, 3 kVmiddotA, four-pole, 50 Hz saturated synchronous generator.     

Online Parameter Estimation of Round Rotor Synchronous Generators Including Magnetic Saturation

Round rotor synchronous generator parameters are identified from online data measured at the terminals of the machine. Parameter estimation results from two generators are presented. Data sets at different operating points are considered to examine the consistency of the proposed method at varying operating conditions. A magnetic saturation model is implemented in the estimation procedure to account for the effect of saturation on generator inductances. Inclusion of saturation in the machine model is found to improve the estimation results. Noise filtering and bad data detection and rejection techniques are employed to increase the reliability of the estimates. An observer is used to estimate the damper winding currents that are otherwise unknown. The estimated parameters are compared to available manufacturer data and the accuracy of the method is assessed.     

Analysis of the voltage distribution in a motor stator winding subjected to steep-fronted surge voltages by means of a multiconductor lossy transmission line model

In this paper, the effect of steep-fronted voltage waveshapes infringing on a pulse-width-modulated (PWM) inverter fed induction motor is studied. The system, composed of a feeder cable and a stator winding, is modeled and simulated by using multiconductor transmission line theory in order to predict the voltage distribution among the coils of the stator winding. A recently developed time-domain equivalent circuit is used; it allows one to correctly describe the dielectric losses and the skin-effect in the conductors. The relationship among the voltage distribution inside the electrical insulation and parameters like the rise time of the applied voltage, the cable length, and the distributed losses is deeply discussed. Good agreement has been found among experimental and numerical results.     

Characterising the d-axis machine model of a turbogenerator usingfinite elements

An analysis of a long established fundamental assumption is presented. The assumption that superposition is valid in frequency response derived models is shown to be wrong, because eddy current losses in the solid rotor cannot be superimposed in the machine direct-axis. This implies that network theory is not valid in characterising the d-axis machine model. A machine model structure with one damper winding in the d-axis is derived from finite element analysis. Unequal mutual inductances in the machine d-axis are determined and hence the so-called differential leakage inductances are found and they are frequency dependent. The study is made on a 150 MVA turbine generator by simulating the standstill frequency response test with finite elements     

Synchronous generator model identification and parameter estimation from operating data

A novel technique to estimate and model parameters of a 460-MVA large steam turbine generator from operating data is presented. First, data from small excitation disturbances are used to estimate linear model armature circuit and field winding parameters of the machine. Subsequently, for each set of steady state operating data, saturable inductances L/sub ds/ and L/sub qs/ are identified and modeled using nonlinear mapping functions-based estimators. Using the estimates of the armature circuit parameters, for each set of disturbance data collected at different operating conditions, the rotor body parameters of the generator are estimated using an output error method (OEM). The developed nonlinear models are validated with measurements not used in the estimation procedure.     

励磁调节对水力发电机组过渡过程的影响分析

为深入研究励磁调节对水力发电机组过渡过程的影响,在Matlab/Simulink平台上,采用面向对象的程序设计技术,建立了包括水力、机械及电气部分的联合计算模型,研究了机组并入不同容量的电力系统时,励磁调节和电力系统稳定器(PSS)对机组频率波动特性和水力过渡过程的影响。计算结果表明,在有限容量的电力系统中,机组安装励磁调节和PSS除了能有效地对无功功率和电压进行调节之外,对机组频率波动也有良好的改善作用,对调压室水位波动有一定的抑制作用,有利于提高电能质量。     

并网异步风力发电机组模型及参数对其暂态稳定性的影响

建立了笼型异步发电机考虑定子电磁暂态的详细模型、忽略定子电磁暂态的简化模型、同时忽略定转子电磁暂态的稳态模型以及一个和两个质量块的风力机轴系模型.针对上述不同组合的5个风力发电机组模型,利用Matlab/Simulink对发电机端部发生三相短路故障情况下的机组暂态行为进行了仿真比较,并通过时域仿真求取了风力机组不同模型下机组故障临界切除时问.结果表明,采用不同风力机组模型对机组暂态稳定性分析结果有很大影响,发电机简化模型和两个质量块的风力机轴系模型较为合适.最后,以提出的合适模型为例,详细研究了风力机模型参数对机组暂态稳定性的影响.