This paper proposes and investigates an innovative methodology that can have a significant impact on the market potential of wound field, small-medium size synchronous generators. The technique proposed here is aimed at removing the need for the traditional stator skewing that is so commonly used in synchronous generators to achieve acceptable values of voltage total harmonic distortion. To do this, a non-standard damper cage configuration is proposed that comprises modulation of the damper bars' positioning. An off-the-shelf, 400kVA generator is used as a benchmark machine. Its rotor is optimized and modified according to the proposed technique. The results of the final machine are then compared to the benchmark machine highlighting the excellent advantages that can be achieved through this technique. A full-scale prototype of the modified generator is then built to experimentally validate the concept. Finally, a detailed analysis on all the performance aspects of the prototype is done, to guarantee that the proposed technique has no negative impact whatsoever on the generator's performance.

This paper provides a comprehensive literature review of techniques for harmonic related power quality improvement of electrical generation systems. An increasing interest in these aspects is due to the ever more stringent power quality requirements, deriving from new grid codes and compliancy standards, aimed at limiting waveform harmonic distortion at all points of the distribution network. Although a wealth of literature is available for such techniques, it has never been compiled into a handbook incorporating all the solutions aimed at both electrical machine and power systems engineers. IntroductionIn the world of electrical power generation, a main point of consideration has always been to achieve adequate performance in terms of power quality. In this context, an important factor is the generation, management and reduction/compensation of spatial and time harmonics throughout the whole power system. From the first developments in the mid-1800s of electrical power generation and distribution systems, harmonic content improvement and reduction has evolved from a localised generator design problem to an internationally regulated supply characteristic that must be considered at all points of the power distribution network.This paper is thus aimed to be a review of harmonic improvement techniques and methodologies, organised to follow and indicate the development timeline of these methods. Distribution level generation has been chosen as the focus to align with recent changes in grid topology caused by distributed and renewable generation. In this section, the paper begins by detailing the changing nature of power quality in distribution networks followed by a description of the main types of power quality issues and an overview of the key standards governing network limits. The focus then shifts to harmonic reduction procedures and methodologies. A review of harmonic reduction methods based around the design of rotating electrical generators is developed, followed by a review of modern methods applied to new generation systems, such as renewable sources.

-Although power quality aspects of electrical machines have been extensively studied and investigated for a large number of years, room for improvement still exists in the field of classic, wound-field, synchronous generators. This paper proposes an innovative method of power quality improvement for single-phase synchronous generators in which the usual DC field current is replaced by a calculated current waveform. The optimised field current waveform is designed in such a way that harmonics created by the machine geometry and the winding configuration are significantly reduced.

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The excitation system of the wound field synchronous machine has remained largely unchanged over the past 50 years. Nonetheless there has been significant research into exciterless solutions which, through integration of the excitation system with the main machine, aim to offer improved power density, simplified manufacture, and better cooling opportunities. This work presents the history of exciterless solutions for wound-field synchronous machines focusing on the challenges for medium power generators. The very latest innovations are discussed, signposting the future for the exciterless machine along with new challenges and opportunities for engineers.

The replacement of the brushless exciter in the synchronous generator has long been desired as a method to increase power density. There are many topologies available that allow the excitation system of a synchronous generator to be combined with the main magnetic circuit, but these topologies have previously only been demonstrated on low power machines. This paper develops an analytical model of an existing exciterless machine topology and uses it to produce an optimized winding configuration to convert an existing, brushless exciter based, generator design to exciterless. Harmonic performance is a key requirement for medium power designs, with strict restrictions placed on manufacturers by grid standards worldwide. Therefore, the focus of the analytical model is to accurately predict the harmonic content of the machine at no-load, including the overall output voltage shape. This is validated experimentally against a prototype machine, and the feasibility of the exciterless topology, for medium power and above applications, is discussed.