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.

The Aesthetics Of Paul Verlaine And Changampuzha Krishnapillai - A Comparative Perspective

The present study is entitled The Aesthetics of Paul Verlaine and Changampuzha Krishnapillai - a comparative perspective. The purpose of the study is to compare the poetic genius of the French poet Paul Verlaine (1844-1896) and that of the Malayalam poet Changampuzha Krishnapillai (1911-1948), within a descriptive framework. The investigation will hopefully answer the questions- Has Changampuzha been indeed influenced by Verlaine, if so, to what extent? Can the aesthetic appreciation be justified in both poets as illustrated in their works? The comparative methodology of juxtaposing the selected oeuvres of the poets is largely adopted in the study. Since the span of analysis is across national and linguistic borders, the distinguishing as well as exclusive traits of the individual poets will be of much importance in formulating the comparative assumption in this work. The vastly differing geographical, linguistic and cultural milieus of these two poets,-one a national French poet and the other, a regional Indian poet writing in Malayalam prima facie,endow the theme of the dissertation with an innate hue of diversity. Such an ambitious task would naturally entail a renewed research into the dedication of the poets to their muses and their ultimate contributions to poetics. The analysis, while attempting to illuminate from a fresh angle, the amply researched oeuvre of Verlaine and the lesser studied one of Changampuzha, cannot but be aware of the limitations of the task at hand. The present study is the first of its kind on the specific theme of analysis, and is hoped that it would be of relevance since no work has so far been known to have been undertaken on the topic. At a time when the birth centenary celebrations of Changampuzha have just concluded, this study is hoped to assume significance as it would help in isolating the originality of the poet's works, extricating the garb of the French influence. Ultimately, this study aims at creating a wider appreciation of the impact that the French writers have had on Malayalam writers, thus shedding new light on the benign foreign influences that served to enhance the beauty of our cultural heritage