Damper cage loss reduction and no-load voltage THD improvements in salient-pole synchronous generators

Salient-pole synchronous generators (SG) have a long history of utilization as reliable power generation systems. Important aspects of such generators include a high power-to-weight ratio, high efficiency and a low cost per kVA output [1]. Another critical aspect is the requirement for very low harmonic content in the output voltage. Hence, it is very important to be able to model and predict the no-load voltage waveform in an accurate manner in order to be able to satisfy standards requirements, such as the permissible total harmonic distortion (THD). Also, at steady-state conditions, parasitic voltages are induced in the damper bars which lead to a current flow with associated power losses and an increase in temperatures. This paper deals with an in-detail analysis of a 4 MVA SG, whose operation is studied and compared with experimental results for validation purposes. The same platform is then used to propose innovative solutions to the existing design and operational challenges of the machine aimed at reducing ohmic loss in the damper cage and improving the output voltage THD, without reverting to disruptive techniques such as rotor and/or stator skewing

Simplified Damper Cage Circuital Model and Fast Analytical–Numerical Approach for the Analysis of Synchronous Generators

The long and enduring history of utilization of the wound-field synchronous generator in a large number of applications makes it one of the most known and consolidated electrical machine technologies. Thus, its design, modeling, and analysis processes have been widely exploited and implemented through various and different methods, including the equivalent circuit approach. When a damper cage is embedded within the rotor of the synchronous generator, its theoretical analysis becomes quite complicated. Thus, today numerical tools are being used. In this paper, an alternative way of modeling symmetric damper cages of salient-pole synchronous generators is presented. The proposed approach is embedded in the circuital model of the generator. A hybrid analytical-numerical model is implemented, permitting to accurately predict the voltage waveforms of the generator with excellent accuracy, however, at a lower cost of computational resources than the pure numerical method. A case study of an off-the-shelf 400 kVA machine is considered to develop and validate the proposed technique. The results are compared with the corresponding finite-element and experimental evaluations for validation purposes

Advances in Modelling and Control of Wind and Hydrogenerators

Rapid deployment of wind and solar energy generation is going to result in a series of new problems with regards to the reliability of our electrical grid in terms of outages, cost, and life-time, forcing us to promptly deal with the challenging restructuring of our energy systems. Increased penetration of fluctuating renewable energy resources is a challenge for the electrical grid. Proposing solutions to deal with this problem also impacts the functionality of large generators. The power electronic generator interactions, multi-domain modelling, and reliable monitoring systems are examples of new challenges in this field. This book presents some new modelling methods and technologies for renewable energy generators including wind, ocean, and hydropower systems

Improved damper cage design for salient-pole synchronous generators

The benefits of implementing a damper winding in salient-pole, synchronous generators are widely known and well consolidated. It is also well known that such a winding incurs extra losses in the machine due to a number of reasons. In order to improve the overall efficiency and performance of classical salient-pole, wound field, synchronous generators that employ the traditional damper cage, an improved amortisseur winding topology that reduces the inherent loss is proposed and investigated in this paper. This is essential in order to meet modern power quality requirements and to improve the overall performance of such ’classical’ machines. The new topology addresses the requirements for lower loss components without compromising the acceptable values of the output voltage total harmonic distortion and achieves this by having a modulated damper bar pitch. As vessel for studying the proposed concept, a 4MVA, salient-pole, synchronous generator is considered. A finite element model of this machine is first built and then validated against experimental results. The validated model is then used to investigate the proposed concept with an optimal solution being achieved via the implementation of a genetic algorithm optimization tool. Finally, the performance of the optimised machine is compared to the original design both at steady state and transient operating conditions

Advances in Modelling and Control of Wind and Hydrogenerators

Rapid deployment of wind and solar energy generation is going to result in a series of new problems with regards to the reliability of our electrical grid in terms of outages, cost, and life-time, forcing us to promptly deal with the challenging restructuring of our energy systems. Increased penetration of fluctuating renewable energy resources is a challenge for the electrical grid. Proposing solutions to deal with this problem also impacts the functionality of large generators. The power electronic generator interactions, multi-domain modelling, and reliable monitoring systems are examples of new challenges in this field. This book presents some new modelling methods and technologies for renewable energy generators including wind, ocean, and hydropower systems

A fast method for modelling skew and its effects in salient-pole synchronous generators

The general effects of implementing skewing techniques in electrical machines are well known and have been extensively studied over the years. An important aspect of such techniques is related to the identification of optimal methods for analyzing and modelling any skewed components. This paper presents a fast, finite-element-based method, able to accurately analyze the effects of skew on wound-field, salient-pole synchronous generators in a relatively shorter time than the more traditional methods. As vessel for studying the proposed technique, a 400kVA alternator is considered. Analytical and theoretical considerations on the benefits of skewing the stator in the generator under analysis are preliminary carried out. A finite-element model of the machine is built and the proposed method is then implemented to investigate the effects of the skewed stator. Comparisons against more traditional techniques are presented, with focus on the analysis of the voltage total harmonic distortion and the damper bars’ currents. Finally, experimental tests are performed at no-load and on-load operations for validation purposes, with excellent results being achieved

Електромагнітні процеси у демпферній системі роторів гідрогенераторів при нерівномірності повітряного проміжку

Зазначено, що за тривалої експлуатації потужних гідрогенераторів виникає нерівномірність повітряного проміжку між статором і ротором, внаслідок чого в полюсах ротора спостерігаються пульсації магнітного потоку, а в стержнях демпферної системи ротора протікають індуковані струми. Розподіл струмів між стержнями є нерівномірним, що спричиняє значні термомеханічні деформації демпферної системи та пульсуючі електромагнітні сили, що діють на її стержні. Оскільки відомі технічні заходи для підтримки рівномірності проміжку в гідрогенераторах є недостатньо ефективними, необхідно удосконалення демпферних систем для підвищення їх стійкості. Розроблено нову математичну модель, проаналізовано фізичні процеси та виявлено основні причини підвищеної пошкоджуваності демпферної системи за наявності ексцентриситету ротора. Запропоновано технічні рішення, які суттєво зменшують термомеханічні деформації та пульсуючі сили в стержнях ротора.При длительной эксплуатации мощных гидрогенераторов возникает неравномерность зазора между статором и ротором, в результате чего в полюсах ротора возникают пульсации магнитного потока, а в стержнях демпферной системы протекают индуцированные токи. Распределение токов между стержнями неравномерно, что вызывает термомеханические деформации демпферной системы и пульсирующие электромагнитные силы, действующие на ее стержни. Поскольку известные меры по поддержанию равномерности зазора недостаточно эффективны, необходимо усовершенствование демпферных систем для повышения их устойчивости. Разработана новая математическая модель, проанализированы физические процессы и установлены основные причины повышенной повреждаемости демпферной системы при наличии эксцентриситета ротора. Предложен ряд технических решений, которые существенно уменьшают термомеханические деформации и пульсирующие силы в стержнях ротора.With prolonged use of powerful hydro generators appears uneven air gap between the stator and rotor. It resulting in pulsation of the magnetic flux in the rotor poles, and in the rotor bars flow induced currents. The distribution of induced current between the rods is uneven. It’s causing extensive thermo mechanical deformations of the rods and appears pulsating electromagnetic forces, acting on rods. Known technical measures for maintaining uniformity of air gap in hydro generators are not effective. Therefore it is necessary improvements of the system rods of rotor of hydro generators to enhance its resilience. A new mathematical model was worked, the physical processes were analyzed and the main causes of damage of the rotor damper system with the presence of the rotor eccentricity were researched. A number of technical solutions for significantly reducing the negative thermo mechanical deformations and pulsating forces in the rotor rods was proposed

An investigation into the effects of load modeling of transient stability and analysis of voltage collapse

Bibliography: leaves 187-193.The aim of this thesis is to investigate the effects of load modeling on transient stability studies and to analyze the phenomenon of voltage collapse. In addition, the different generator models are compared and the effects of voltage dips on induction motor performance are investigated. The modeling of loads dates back to the late forties when network analyzers were still in use. The prohibitive computational requirements resulted in many approximations being made to the load models. In turn, this resulted in the use of simple models which did not provide sufficient information about the dynamic behavior of loads. With the advent of digital computers, more accurate load models could be used in dynamic simulations. Despite this improvement in computational tools, the problem of load modeling for stability studies is still very complex. The load composition changes with the time of the day, the consumer's lifestyle, weather, state of the economy and other factors. The accurate load model would include amongst other things, the effects of the abovementioned factors. Since these factors are unpredictable, accurate load modeling becomes very complex indeed. It is mainly for these reasons that the approximate are still widely in use. Ideally, the response of these approximate models should be compared to the actual loads under similar disturbances. A further concern of the thesis is the study of voltage stability. The voltage stability problem has become a matter of growing concern amongst bulk transmission utilities worldwide over the last decade. For long, the stability of a power system was related exclusively to the synchronous stability of the generators

Advances in Modelling and Control of Wind and Hydrogenerators

Rapid deployment of wind and solar energy generation is going to result in a series of new problems with regards to the reliability of our electrical grid in terms of outages, cost, and life-time, forcing us to promptly deal with the challenging restructuring of our energy systems. Increased penetration of fluctuating renewable energy resources is a challenge for the electrical grid. Proposing solutions to deal with this problem also impacts the functionality of large generators. The power electronic generator interactions, multi-domain modelling, and reliable monitoring systems are examples of new challenges in this field. This book presents some new modelling methods and technologies for renewable energy generators including wind, ocean, and hydropower systems

Modélisation des machines par circuits couplés pour l'observation des courants de barres au rotor

Ce travail présente une modélisation rapide d’ordre élévé capable de modéliser une configuration rotorique en cage complète ou en grille, de reproduire les courants de barre et tenir compte des harmoniques d’espace. Le modèle utilise une approche combinée d’éléments finis avec les circuits-couplés. En effet, le calcul des inductances est réalisé avec les éléments finis, ce qui confère une précision avancée au modèle. Cette méthode offre un gain important en temps de calcul sur les éléments finis pour des simulations transitoires. Deux outils de simulation sont développés, un dans le domaine du temps pour des résolutions dynamiques et un autre dans le domaine des phaseurs dont une application sur des tests de réponse en fréquence à l’arrêt (SSFR) est également présentée. La méthode de construction du modèle est décrite en détail de même que la procédure de modélisation de la cage du rotor. Le modèle est validé par l’étude de machines synchrones: une machine de laboratoire de 5.4 KVA et un grand alternateur de 109 MVA dont les mesures expérimentales sont comparées aux résultats de simulation du modèle pour des essais tels que des tests à vide, des courts-circuits triphasés, biphasés et un test en charge.This work presents a fast high-order model able to model a rotor configuration in full cage or grid, reproduce bar currents and consider the space harmonics. The model is based on a Combination of Finite Element method and Coupled Circuits. Indeed, the calculation of inductances is performed with magnetostatic finite element resolutions which gives to the model an advanced accuracy.This method offers a significant gain in computing time on finite element for transient simulations. Two simulation tools are developed, one in time domain for dynamic resolutions and another in phasor domain whose application on StandStill Frequency response (SSFR) is also presented. The model construction method is described in detail as well as the modeling procedure of the rotor circuit. The model is validated by the study of synchronous machines: a laboratory machine of 5.4 KVA and a large hydrogenerator of 109 MVA whose experimental measurements are compared to the model simulation results for tests such as no-load, three-phase and two-phase short circuit and also a load test