Salient Pole Synchronous Generator Research Articles

Effect of Field-Voltage Source Impedance on Load-Rejection Test Results of Large-Rating Synchronous Generators

This paper presents a technique to determine the effect of the field-voltage circuit during the load-rejection test of a large-rating salient-pole synchronous generator. Once the circuit powered by a six-pulse converter connected to the excitation transformer of the generator unit corresponds to a power-supply voltage not constant immediately after the load rejection, a careful evaluation of the resulting signals is necessary to extract rotor and stator parameters from the comparison with theoretical expressions derived under the assumption of constant-field terminal voltage and excluding external effects. The results obtained in the load-rejection test of a 179-MVA, 13.8-kV generating unit at Nova Ponte power plant show the parameters that are more affected by the external impedance in series with the rotor circuit and how to compensate them.

A salient‐pole synchronous generator with permanent magnets between the field poles

AbstractIn this paper, a new salient‐pole synchronous generator (SG) termed the PMa‐SG is presented. In the PMa‐SG, permanent magnets (PMs) are placed between the pole shoes to reduce the magnetic saturation in the field poles. By using finite element analysis (FEA), the internal magnetic fields and basic characteristics of a 2.8‐MVA PMa‐SG are compared with those of a conventional SG of the same size, and the reduction effect of the magnetic saturation of the PMs is examined. The FEA simulations are also validated by experiments on a 2.0‐kVA prototype machine. The PMs placed between the pole shoes reduce the magnetic saturation in the pole bodies and pole tips and effectively increase the terminal voltage and output power. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 174(4): 58–67, 2011; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21132

Steady-State Analysis of a Permanent-Magnet-Assisted Salient-Pole Synchronous Generator

This paper presents a simple mathematical model for the steady-state analysis of a permanent-magnet-assisted salient-pole synchronous generator (PMa-SG). The PMa-SG is a new type of salient-pole SG that has PMs between the adjacent pole shoes. The developed model takes into account the magnetic saturation and core loss, and enables quantitative predictions of load characteristics from the no-load test data. The validity of the developed model is confirmed experimentally. The effect of the PMs on the performance characteristics of the PMa-SG is also investigated.

Detection of inter-coil short circuits in coils of salient pole synchronous generator field winding on the basis of analysis of magnetic field in the machine

Detection of inter-coil short circuits in coils of salient pole synchronous generator field winding on the basis of analysis of magnetic field in the machine

Electromagnetic Field Analysis for Assist Effects of Permanent Magnets in Salient-Pole Synchronous Generators

The assist effects of the permanent magnets in salient-pole synchronous generators are investigated by the electromagnetic field analysis. The flux and voltage are separated by the finite element analyses due to their origins. The measured and calculated results are compared in order to verify the calculation. It is revealed that there are two assist effects of the magnets on the improvement of the generator characteristics. One effect is the reduction in the size of the saturated region at the rotor core. The other effect is the direct flux linkage with the armature windings. The former effect is dominant at the rated load condition. The latter effect increases when the rotor core is oversaturated and compensates for the decrease in the former effect.

TIME-STEPPING FINITE-ELEMENT ANALYSIS OF DYNAMIC ECCENTRICITY FAULT IN A THREE-PHASE SALIENT POLE SYNCHRONOUS GENERATOR

In this paper, two-dimensional time-stepping flnite- element (TSFE) method is performed for modeling and analyzing of a salient pole synchronous generator with difierent degree of dynamic eccentricity (DE) fault. TSFE analysis is used to describe the in∞uence of DE fault on the ∞ux distribution within the generator and no-load voltage proflles at low and high fleld current is obtained for healthy and faulty cases. Comparing the magnetic ∞ux distribution of healthy and faulty generators helps to detect the in∞uence of DE fault. Also, it can be seen at no-load condition with low excitation current, the efiect of the eccentricity is considerable compared to that of the rated excitation current. Since the calculation of inductances of the machine is the most

Determination of Load Angle for Salient-pole Synchronous Machine

This paper presents two methods for load angle determination for salient-pole synchronous generator. The first method uses optical encoder to detect the rotor position. In some cases the end of the rotor shaft is not free to be used and mounting of an encoder is impossible. Therefore, the second method proposes estimation of the load angle based on the measured electrical values that have been already used in excitation control system of the synchronous generator. Estimation method uses corresponding voltage-current vector diagram and parameters of the synchronous generator, transformer and transmission lines. Both methods were experimentally verified on the digital control system and synchronous generator connected to power system. The estimation and measured results were compared. The accuracy of load angle estimation method depends on voltage and current measurement accuracy as well as generator, transformer and transmission line parameter accuracy. The estimation method gives satisfactory accuracy for load angles less than 120o el. Thus, it can be applied in excitation control system to provide stable work of synchronous generator in under-excitation operating area.

Modeling and Simulation of Internal Faults in Salient-pole Synchronous Generators with Wave Windings

When an internal fault occurs in the wave-connected windings of salient-pole synchronous generators, the symmetry between the parallel windings is broken, and different currents flow in them since unsymmetrical magnetic linkage exists between the stator windings. The aim of this article is to present a model to investigate the internal fault currents in large hydrogenerators with wave windings. This model is based on a modified winding function approach, where the machine inductances are calculated directly from the machine winding distribution, and the space harmonics produced by them are also taken into account. The calculation of the machine inductances are made easier by the use of machine electrical parameters instead of geometrical parameters. The fast Fourier transform analysis of the simulated results has been tabulated for different cases of internal faults. By using the simulated internal fault data, suitable numerical protection schemes for hydrogenerators can be developed.

極間に永久磁石を挿入した突極形同期発電機

In this paper, a new salient-pole synchronous generator (SG) termed the PMa-SG is presented. In the PMa-SG, permanent magnets (PMs) are placed between the pole shoes to reduce the magnetic saturation in the field poles. By using finite element analysis (FEA), the internal magnetic fields and basic characteristics of a 2.8-MVA PMa-SG are compared with those of a conventional SG of the same size, and the reduction effect of the magnetic saturation of the PMs is examined. The FEA simulations are also validated by experiments on a 2.0-kVA prototype machine. The PMs placed between the pole shoes reduce the magnetic saturation in the pole bodies and pole tips and effectively increase the terminal voltage and output power. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 174(4): 58–67, 2011; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21132

Weight optimisation of a salient pole synchronous generator by a new genetic algorithm validated by finite element analysis

In this study, a new approach for genetic algorithm (GA) is proposed and compared with conventional GA (CGA) in the weight optimisation of a 2-MVA salient pole synchronous machine. The main differences between the two algorithms are that, in the newly proposed method, individuals are paired and crossed over based on the Mendelian rules of genetics, and the mutation operator is omitted. The rules concern the segregation of Alleles and the independent assortment of Alleles. This approach is comprehensive and conceptually accurate since its framework uses Mendelian population genetics. The operation CPU time is longer in the new approach when compared to the conventional one but can be ignored in electric machine design since it is not a real-time process. The results of the analytic solution and the new and CGA implementation methods are compared in terms of weight, efficiency and temperature. The results obtained are similar to those of the conventional ones and even better in some cases. A finite element analysis (FEA) is done to realise the machine designs optimised by the new GA (NGA) and CGA for the case of a fixed 24-pole design. Hence the improvement over CGA achieved by NGA has been validated through FEA.

Operation of synchronous generator under the influence of time and space harmonics

In stability studies, it is necessary to compute the initial steady-state values of synchronous machine variables as a function of non-sinusoidal terminal quantities. In this paper, the impact of current time and inductance space harmonics on the steady state operation and load angle of synchronous generator is investigated. A nonlinear model of salient-pole synchronous generator based on the abc-frame of reference in harmonic domain is used to investigate the impact of harmonics on the stator flux. It is shown that the fundamental component of stator flux contains additional terms due to the interaction between time and space harmonics. Park transformation is applied to this modified fundamental stator flux to compute the load angle. Simulation results provide new information about the steady-state operating point of synchronous generator under harmonically polluted operating conditions. It is also shown that damper windings and current harmonics phase angles have considerable effects on the operation of synchronous generator.

Magnetic Saturation Effects in a Synchronous Generator During Unbalanced Faults

This paper reviews a phase-domain synchronous generator model and investigates the effects of the non-uniform air gap saturation on the performance of a three-phase salient pole synchronous generator during a single-phase-to-ground short circuit. Accurate representation of magnetic saturation effects in synchronous machines is required when studying their behavior closely. Modeling a synchronous machine directly in the physical phase-domain instead of the dqo-coordinates permits an easy and accurate representation of magnetic saturation in the machine. The reviewed model has been verified to be accurate and effective in representing the behavior of synchronous generators. The test results have showed the strong impact of the non-uniform air gap on the magnetic saturation in a three-phase salient pole synchronous generator.

Computation of the no-load voltage waveform of laminated salient-pole synchronous generators

This paper presents a combined analytical and finite-element (FE) method for computation of the no-load voltage waveform of laminated salient-pole synchronous generators. The described method takes into account saturation effects as well as the damper bar currents due to the slot pulsation field. The method calculates first the damper bar currents and then includes them in the calculation of the no-load voltage. The combination of magnetostatic two-dimensional (2-D) FE simulations for calculating the magnetic coupling between the machine windings and of an analytical resolution results in a very precise prediction of the no-load voltage. At the same time, simulation time is drastically reduced compared with transient magnetic 2-D FE simulations. The method was verified on several examples, comparing the obtained results (damper bar currents and no-load voltage) with results obtained from transient magnetic FE simulations and, in one case, with the measured no-load voltage.

Eddy current heating in large salient pole generators

PurposeThe purpose of the paper is to investigate pole face heating in large, salient pole generators and establish a modelling procedure for accurate rotor pole heat loss computation using finite element analysis.Design/methodology/approachFinite element‐based simulations of the dynamic electromagnetic problem in an idealized 60 Hz, six‐pole, three‐phase generator were carried out, including coupling to three‐dimensional finite element thermal analysis.FindingsThe effect of trailing pole face heating was effectively demonstrated. Accurate estimates of the ventilation and convective cooling were shown to be particularly important.Research limitations/implicationsAccurate heat transfer values could only be obtained using a very sophisticated model in a computational fluid dynamics analysis software package. The complexity of the stator end winding alone makes this a daunting challenge, without the inclusion of the rotation effects and stator cooling ducts. At this stage, it was deemed more useful to use the thermal analysis to observe trends.Practical implicationsThree‐dimensional effects are significant and require modelling. However, obtaining steady state behaviour using a 3D analysis is probably not viable yet. The synchronous operating conditions were obtained from a two‐dimensional analysis and used as the initial conditions for a full 3D analysis.Originality/valueThe paper has helped to enhance the understanding of pole face heat loss in large salient pole synchronous generators, fully examining the mechanisms causing the heating. A complete procedure to achieve this task in a realistic time frame using sophisticated finite element analysis tools has been proposed.

Improved Transient Simulation of Salient-Pole Synchronous Generators With Internal and Ground Faults in the Stator Winding

An improved model for simulating the transient behavior of salient-pole synchronous generators with internal and ground faults in the stator winding is established using the multi-loop circuit method. The model caters for faults under different ground conditions for the neutral, and accounts for the distributed capacitances of the windings to ground. Predictions from the model are validated by experiments, and it is shown that the model accurately predicts the voltage and current waveforms under fault conditions. Hence, it can be used to analyze important features of faults and to design appropriate protection schemes.

Determination of a synchronous generator characteristics via Finite Element Analysis

In the paper a determination of characteristics of a small salient pole synchronous generator (SG) is presented. Machine characteristics are determined via Finite Element Analysis (FEA) and for that purpose is used the software package FEMM Version 3.3. After performing their calculation and analysis, one can conclude that most of the characteristics presented in this paper can be obtained only by using the Finite Element Method (FEM).

A tool for extracting synchronous machines parameters from the dc flux decay test

A novel computer system tool for the parameter estimation of mathematical synchronous-machine models is presented. It uses state-of-the-art information technology software. The tool allows the electrical power engineers to obtain the electrical parameters of a synchronous machine model. The practical usefulness of the developed system is demonstrated by obtaining the parameter set for conventional and high order d and q axis models from the dc flux decay test. The two-axis model parameters are estimated with the well-known maximum likelihood algorithm. The user can also validate its set of estimated parameters against experimental data. Consequently, a better behavior prediction of synchronous generators within a power system can be achieved. The tool was developed using LabVIEW as a software environment and a low cost data acquisition card, which has a user friendly interface. A solid salient-pole synchronous generator of 7 kVA was used to illustrate its practical impact of the proposed system, where acceptable accuracy in the set of estimated parameters was achieved.

Modeling and Simulation of a Salient-Pole Synchronous Generator With Dynamic Eccentricity Using Modified Winding Function Theory

This paper models and simulates a salient-pole synchronous generator using a modified winding function theory and more precise stator and rotor winding distribution with dynamic eccentricity between the stator and rotor. Air-gap permeance is also computed more accurately compared to currently available methods. Inductances with this method are compared to those obtained from other methods and it is shown that the results are closer to those obtained from finite element computations. Finally, the calculated inductances are used in a coupled electromagnetic model for simulation and studying the frequency spectrum of the stator line current in the presence of dynamic eccentricity.

Analytic calculation of the voltage shape of salient pole synchronous generators including damper winding and saturation effects

A novel analytic method for determining the no‐load voltage shape of salient pole synchronous generators is presented. The algorithm takes into account the full influence of the damper winding and the saturation effects in the stator teeth. Main interest is an easy and very fast calculation method, which can be used as a criteria for the selection of the number of stator winding slots in the initial design calculation or an optimization process. The analytical results obtained are compared with the results of transient finite element analyses.

Harmonic analysis of output voltage in synchronous generator using finite-element method taking account of the movement

This paper discusses implementation of a method for analysis of the harmonic distortion factor of output voltage in a synchronous generator. A two-dimensional finite-element modeling is used for calculating the stator coil flux linkages and consideration is given to rotor movement. The treatment of the motion employs the moving-band technique. To illustrate the proposed method, the distortion factor of the output voltage waveform in a 150 kW salient pole synchronous generator has been computed and found to be consistent with experimental results.