FEM based Virtual Prototyping and Design of Third Harmonic Excitation System for Low Voltage Brushless Alternators

Salient pole brushless alternators coupled to IC engines are extensively used as stand-by power supply units for meeting in- dustrial power demands. Design of such generators demands high power to weight ratio, high e ciency and low cost per KVA out- put. Moreover, the performance characteristics of such machines like voltage regulation and short circuit ratio (SCR) are critical when these machines are put into parallel operation and alterna- tors for critical applications like defence and aerospace demand very low harmonic content in the output voltage. While designing such alternators, accurate prediction of machine characteristics, including total harmonic distortion (THD) is essential to mini- mize development cost and time. Total harmonic distortion in the output voltage of alternators should be as low as possible especially when powering very sophis- ticated and critical applications. The output voltage waveform of a practical AC generator is replica of the space distribution of the ux density in the air gap and several factors such as shape of the rotor pole face, core saturation, slotting and style of coil disposition make the realization of a sinusoidal air gap ux wave impossible. These ux harmonics introduce undesirable e ects on the alternator performance like high neutral current due to triplen harmonics, voltage distortion, noise, vibration, excessive heating and also extra losses resulting in poor e ciency, which in turn necessitate de-rating of the machine especially when connected to non-linear loads. As an important control unit of brushless alternator, the excitation system and its dynamic performance has a direct impact on alternator's stability and reliability. The thesis explores design and implementation of an excitation i system utilizing third harmonic ux in the air gap of brushless al- ternators, using an additional auxiliary winding, wound for 1=3rd pole pitch, embedded into the stator slots and electrically iso- lated from the main winding. In the third harmonic excitation system, the combined e ect of two auxiliary windings, one with 2=3rd pitch and another third harmonic winding with 1=3rd pitch, are used to ensure good voltage regulation without an electronic automatic voltage regulator (AVR) and also reduces the total harmonic content in the output voltage, cost e ectively. The design of the third harmonic winding by analytic methods demands accurate calculation of third harmonic ux density in the air gap of the machine. However, precise estimation of the amplitude of third harmonic ux in the air gap of a machine by conventional design procedures is di cult due to complex geome- try of the machine and non-linear characteristics of the magnetic materials. As such, prediction of the eld parameters by conven- tional design methods is unreliable and hence virtual prototyping of the machine is done to enable accurate design of the third har- monic excitation system. In the design and development cycle of electrical machines, it is recognized that the use of analytical and experimental methods followed by expensive and in exible prototyping is time consum- ing and no longer cost e ective. Due to advancements in com- putational capabilities over recent years, nite element method (FEM) based virtual prototyping has become an attractive al- ternative to well established semi-analytical and empirical design methods as well as to the still popular trial and error approach followed by the costly and time consuming prototyping. Hence, by virtually prototyping the alternator using FEM, the important performance characteristics of the machine are predicted. Design of third harmonic excitation system is done with the help of results obtained from virtual prototype of the machine. Third harmonic excitation (THE) system is implemented in a 45 KVA ii experimental machine and experiments are conducted to validate the simulation results. Simulation and experimental results show that by utilizing third harmonic ux in the air gap of the ma- chine for excitation purposes during loaded conditions, triplen harmonic content in the output phase voltage is signi cantly re- duced. The prototype machine with third harmonic excitation system designed and developed based on FEM analysis proved to be economical due to its simplicity and has the added advan- tage of reduced harmonics in the output phase voltage.

Matemàtiques a l'educació infantil : fem comparacions.'Matemáticas en Educación Infantil : hacemos comparaciones'.

Se expone una actividad de matemáticas realizada por la escuela de Sineu, Mallorca. Se trata de medir el campanario del pueblo para obtener información real y adaptar las medidas a las necesidades de aprendizaje de los niños des de una visión global tomada de la vida cotidiana. Finalmente, se llevan a cabo una serie de actividades relacionadas con las medidas.

I què fem a casa nostra? Reflexions i experiències sobre esport i immigració.

Se muestran fotografías. Contiene anexo al final del artículo. Resumen tomado del autor

CEIP Santa Gertrudis : aquesta escola la fem tots. 'CEIP Santa Gertrudis : esta escuela la hacemos todos'.

Resumen tomado del autor

Programa d'ajut a la docència universitària : fem camí cap a Europa. 'Programa de ayuda a la docencia universitaria : hacemos camino hacia Europa'.

Se presenta un programa cuyo objetivo es la mejora de la calidad de la docencia universitaria y facilitar su adaptación al nuevo espacio europeo de educación superior. Para ello se presentan cuatro cursos dirigidos al profesorado universitario para adaptarse a los futuros planes de estudio.

Fem quart en dos cursos? : adaptació curricular duta a terme per l'IES Celestí Ballera de Granollers. '¿Hacemos cuarto en dos cursos? : adaptación curricular llevada a cabo por el IES Celestí Ballera de Granollers'.

Teniendo en cuenta que hay alumnado que al acabar tercero de secundaria no está preparado para alcanzar los objetivos finales de etapa, pero sí que es suficientemente maduro para darse cuenta de su realidad y tomar una decisión juntamente con su familia, esta escuela realizó una adaptación curricular para estos estudiantes. Los autores exponen la experiencia de adaptación a la diversidad en la ESO, mencionando aspectos como los recursos que disponían, el marco legal, y como se organiza una adaptación.

Fer memoria a aprendre a escriure sobre allò que fem a l'aula. 'Hacer memoria sobre eso que hacemos en el aula'.

Resumen de las autoras en catalán

Com fem El matí de Catalunya Ràdio. '¿Cómo hacemos El matí de Catalunya Ràdio?'.

Resumen basado en el de los autores en catalán

Fem de periodistes a l'escola : una experiència d'escriptura de notícies a primer de primària. 'Hacemos de periodistas en la escuela : una experiencia de escritura de noticias en primero de primaria'.

Resumen de la autora en catalán

Els joves fem recerca. 'Los jóvenes hacemos investigación'.

Resumen de la revista en catalán

La societat canvia : i a l'escola, qu?? fem?. 'La sociedad cambia : y en la escuela, ??qu?? hacemos?'

Resumen tomado de la publicaci??n en catal??n. Este art??culo forma parte del monogr??fico 'Identitat i diversitat'

Fem el conte de Lola Anglada. 'Hagamos el cuento de Lola Anglada'.

Presentarse a un concurso de ilustración puede convertirse en un medio de motivación y de cohesión grupal. Se explica cómo se hizo un cuento sobre la vida de una persona, de entrada desconocida, que resultó ser fascinante: Lola Anglada.

Fem ràdio. 'Hacemos radio'.

Resumen basado en el de la autora

Què fem a l'estiu. 'Qué hacemos durante el verano'.

Resumen en catalán

L'aventura de la imaginació. Fem monstres amb Joan Perucho. ' La aventura de la imaginación. Hagamos monstruos con Joan Perucho'.

Resumen de los autores