Dissertations / Theses on the topic 'Three-phase electrical machine'

The ever increasing demand for electrical energy has meant that electrical power systems have evolved to be the highly complex networks that are in existence today, where the transient interactions that take place between large synchronous generators have been the focus of advanced research for many decades. More recently, the proliferation of synchronous and asynchronous generators of comparatively small rating, which are not centrally planned, has added new impetus to this area of research. At a time when not only technical but also economic and environmental concerns must be carefully assessed, more realistic models of the individual power plant transient response and its interaction with the rest of the network become mandatory to achieve more accurate analysis of the network operation and prevent wastage of technical and economical resources. The main thrust of this research project is to develop comprehensive models of rotating machinery with which to assess the transient response of electrical power networks that undergo severe unbalanced operation due to faulty conditions developing anywhere in the power network, including the rotating machinery’s windings. To achieve an unrivalled speed of response, a nodal-based model of the electrical power network has been developed, enabling the study of power networks of any size and topological formation with the utmost flexibility and efficiency. The rotating machinery addressed in this research work is the three-phase synchronous generator and the three-phase asynchronous (induction) machine. In multi-machine power systems transient studies, it is common to look at all the rotating machinery in the network as being healthy units having an idealized sinusoidally distributed stator winding – the possibility of a severe unbalanced condition internal to the machine due to internal fault or the effect of space harmonics, has, so far, not been addressed in a multi-machine environment. In this research work, new EMTP type models, with enhanced numerical properties, are constructed for the simulation of internal and external machine fault phenomena with different levels of details including the effects of saturation and space harmonics. Advanced numerical methods are employed to improve on the numerical stability of the network model allowing the use of larger time steps than what otherwise is possible with traditional numerical methods, enabling the new model to execute faster than existing models and yet to exhibit the same degree of numerical accuracy with an unrivalled degree of modelling flexibility. A case in point is an application made to model the transient response of a Variable Frequency Transformer (VFT) undergoing internal faults on its stator side. The rotating machinery models with internal fault representation developed in this research lend themselves to an application in the area of condition monitoring, where a new method is developed to detect internal faults in the stator side of three phase rotating machinery. The method is shown to be highly effective when applied to machines operating in an isolated environment as well as in a multi-machine power system, performing very well when applied to different types of equipment and various kinds of internal faults.

An estimated 30% of the faults in Induction Machine (IM) are related to its stator. These faults are mostly in the form of an Inter-Turn Short Circuit (ITSC) fault i.e., when two winding inside the stator of IM are shorted due to insulation failure. However, ITSC fault can be avoided by detecting them in advance and then scheduling the maintenance of the IM. This thesis studies two methods for detecting this incipient ITSC fault in a three-phase IM and then estimating the stator resistance unbalance due to the ITSC fault. The first method is based on the asymmetry caused in the IM by the ITSC fault. As a result of this asymmetry, the negative sequence components of the stator voltages and the stator currents are generated inside the IM. A healthy IM also have these negative sequence components due to the manufacturing process and the supply voltage unbalances. The characteristics and the compensation methods of these negative sequence components in a healthy IM are discussed. The results show that after compensating the negative sequence components in a healthy machine, they can be used for detecting an ITSC fault and then to calculate the fault quantities as well as the stator resistance unbalances. The second method for detecting an ITSC fault is based on analysing the stator resistance unbalances. A three-phase drive is used to inject DC voltage in the stationary reference frame. The DC current generated by this DC voltage is measured and then by applying Ohm’s law stator phase resistances are calculated. In a healthy IM, the phase resistances are balanced. However, in case of ITSC fault in any of the phases, the phase resistance of that phase deviates from those of the other two phases which can be utilized for detecting ITSC fault.
Uppskattningsvis 30% av alla fel i induktionsmaskiner (IM) är kopplad till dess stator. Dessa fel är i huvudsak Inter-Turn Short Circuit (ITSC)-fel, dvs. två lindningar inom IM:ens stator blir kortsluta pga. ett isoleringsfel. Emellertid kan man undvika ITSC-fel genom att detektera dem i förhand och planera underhåll. Det här examensarbetet undersöker två metoder för att detektera ett förestående ITSC-fel i en tre-fas IM. Den första metoden är baserad på asymmetrin i IM:er pga. ITSC-felet. Resultatet av den här asymmetrin är att en negativ sekvens genereras i IM:ens statorspänning och statorström. En oskadad IM kan också visa dessa negativa sekvenser pga. tillverksprocessen och statorspänningsobalanser. Egenskaperna och kompensationsmetoderna för dessa negativa sekvenser i en oskadad IM kommer att diskuteras. Resultaten visar att efter kompenseringen av de negativa sekvenserna i en oskadad IM, kan de användas för att detektera ITSC-fel och efteråt för att beräkna felstorheter och även statormotståndobalanser. Den andra metoden för att detektera ITSC-fel är baserad på en undersökning av statormotståndobalanser. Ett tre-fas-drivsystem används för att injektera likspänning i den stationära referensramen. Likströmmen som följer av denna likspänning mäts och statorfasmotstånden beräkna efteråt med Ohms lag. I en oskadad IM är fasmotstånden balanserade. Däremot, när ett ITSC-fel uppstår i en fas, avviker fasmotståndet i den felaktiga fasen från de andra två fasernas, vilket kan användas för att detektera ITSC-fel.

In this study, three different programs are developed for the analysis of the three-phase induction motor, single-phase capacitor type induction motor and switched reluctance motor. The programs are developed by using Pascal and C++ programming languages. In the performance calculations of motors, analytical methods are used and these methods are tested for accuracy. These programs have also capabilities to design an optimum motor, which meets a set of performance, material and manufacturing constraints while minimizing the weight or any other defined objective function. In addition, in this study, an optimization tool is used to obtain an appropriate optimization method for the design of different types of motors. The software is tested over different commercial motors. The results illustrates that the performance calculations and optimization approach of the programs lead to good results.

This thesis describes new methods of evaluating the efficiency of three-phase induction machines using synthetic loading. Synthetic loading causes the induction machine to draw full-load current without the need to connect a mechanical load to the machine's drive shaft. The synthetic loading methods cause the machine to periodically accelerate and decelerate, producing an alternating motor-generator action. This action causes the machine, on average over each synthetic loading cycle, to operate at rated rms current, rated rms voltage and full-load speed, thereby producing rated copper losses, iron loss and friction and windage loss. The excitation voltages are supplied from a PWM inverter with a large capacity DC bus capable of supplying rated rms voltage. The synthetic loading methods of efficiency evaluation are verified in terms of the individual losses in the machine by using a new dynamic model that accounts for iron loss and all parameter variations. The losses are compared with the steady-state loss distribution determined using very accurate induction machine parameters. The parameters were identified using a run-up-to-speed test at rated voltage and the locked rotor and synchronous speed tests conducted with a variable voltage supply. The latter tests were used to synthesise the variations in stator leakage reactance, magnetising reactance and the equivalent iron loss resistance over the induction machine's speed range. The run-up-to-speed test was used to determine the rotor resistance and leakage reactance variations over the same speed range. The test method results showed for the first time that the rotor leakage reactance varied in the same manner as the stator leakage and magnetising reactances with respect to current. When all parameter variations are taken into account there is good agreement between theoretical and measured results for the synthetic loading methods. The synthetic loading methods are applied to three-phase induction machines with both single- and double-cage rotors to assess the effect of rotor parameter variations in the method. Various excitation waveforms for each method were used and the measured and modelled efficiencies compared to conventional efficiency test results. The results verify that it is possible to accurately evaluate the efficiency of three-phase induction machines using synthetic loading.

Desenvolvimento de uma máquina síncrona trifásica com ímãs de Nd-Fe-B e núcleo do rotor a partir de ferro sinterizado para aplicação em aerogeradores de 7,5 kW, verificando a viabilidade do protótipo. Partindo de um projeto anteriormente desenvolvido, foi realizada alteração no ângulo das chapas do estator em 10º, com o intuito de minimizar o efeito de correntes parasitas, sendo esse um dos fatores que influenciam os resultados. Para avaliação de desempenho, foi utilizada uma bancada de testes composta de analisador de energia, sensor de torque e instrumentos de medição, sendo o acionamento do protótipo realizado através de um motor de indução controlado por um inversor de frequência. Entre os resultados encontrados, foi constatada a presença de harmônicas que impactam sobre os valores obtidos do protótipo. Os testes realizados, de simulação e parâmetros elétricos, indicaram resultados apropriados ao desempenho de uma máquina elétrica trifásica, porém mostram-se necessárias alterações para um melhor desempenho do protótipo.
Development of a three-phase synchronous machine with Nd-Fe-B magnets and rotor core from sintered iron for application in 7.5 kW wind turbines, verifying the feasibility of the prototype. Starting from a previously developed design, a change in the angle of the stator plates was made in 10º, in order to minimize the effect of the parasite currents, being one of the factors that influence the results. For performance evaluation, a test bench composed of energy analyzer, torque sensor and measuring instruments was used, and the drive of the prototype was carried out through an induction motor controlled by a frequency inverter. Among the results found, it was verified the presence of harmonics that impact on the values obtained from the prototype. The tests performed, simulation and electrical parameters, indicated results appropriate to the performance of a three-phase electric machine, however changes are needed for a better performance of the prototype.

Ce travail apporte une contribution au calcul des machines électriques asynchrones, dans le cas ou une modélisation de type circuits couplés est impossible (rotors massifs ou à cage profonde). La première partie expose les différentes façons de prendre en compte le mouvement. La deuxième partie expose une nouvelle méthode, double entrefer et approximation du premier harmonique d'espace, qui est ensuite développée dans le cas des régimes transitoires, à courants imposés puis à tensions imposées. On montre aussi que la méthode se prête à un couplage avec des circuits électriques extérieurs. Dans la troisième partie, on procède à une validation de la méthode pour deux machines à induction pour lesquelles nous disposions de données expérimentales: une machine triphasée de 950 kW et une machine diphasée de 300 W avec condensateur. Dans la quatrième partie, on prévoit les caractéristiques d'un prototype de machine rapide (100 kW, 30 000 tr/mn) alimenté de différentes manières par deux sortes d'onduleurs. À l'approximation du premier harmonique d'espace, la méthode développée autorise des rotations élémentaires importantes, ce qui correspond à un gain de temps appréciable par rapport au suivi des grandeurs elles mêmes. La méthode peut être affinée par la prise en compte d'harmoniques supérieurs, et elle est généralisable aux cas des machines saturées

The work is focusing on dynamic effects of short-circuit currents, more precisely dynamic effects of short-circuit currents on switchgear cabinet (terminal box). The work was designated to a concrete construction type of two switchgear cabinets located on rotating machines via company Siemens Electric Machines Drásov s.r.o.. The switchgear cabinets are designed for non-explosive environment where the air is used as an insulating medium. The task was to determine how the device will behave during the three-phase short-circuit and three-phase short-circuit with earth/ground connection. The following programs were used for the calculations and simulations: Ansoft Maxwell 16.0, Ansoft Maxwell 2015 and ANSYS Workbench 16.0. By using these programs the effects of forces which acts on current paths in cabinet caused by the passage of short-circuit current were simulated, statically and also dynamically. Further the effects of pressure acting on cabinet frame during the arc short-circuit have been statically and dynamically simulated. All the results are summarized in the conclusion. Conclusion also contains the final evaluation of the functionality of both switchgear cabinets.