Abstract-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 salientpole, 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.

The ever-increasing demand for passenger air traffic results in larger airline fleets every year. The aircraft market forecast reveals an unprecedented growth for the coming decades, leading to serious environmental and economic concerns among airlines and regulatory bodies. Different approaches, for both airborne and ground operations, have been proposed to reduce and control emissions without compromising profit margin. For on-ground activities, the electric taxiing (ET) methodology is one of the suggested solutions for reducing the emissions and the acoustic noise in the airport, and for lowering the fuel consumption and operating costs. This paper thus aims to review and collate the more important literature related to electric taxiing systems (ETSs), in order to draw an inclusive picture regarding the current state of the art of a moving and growing sector that just started its first steps towards an ambitious target. After introducing the general concept of ET, elaborations on the benefits and challenges of available technologies are done with a detailed comparison of the different systems. Finally, recommendations for future research and outlook on ET are presented.

Electrical machines and drives keep moving away from traditional technologies such as brushed machines and wound field machines towards lighter, 'easier to maintain' machines. A very interesting aspect is that certain transport applications, especially the aerospace industry, still favour the classical wound field machine for its main generating system such as the Boeing 787.This paper focuses on investigating this particular trend by presenting a detailed overview of historical power generation systems on aircraft. This paper compares the current state of the art of wound field machines with other generator families. The results of this analysis are then projected into the needs of the electrical power generation and distribution system on aircraft. While power density is a major objective for any aerospace application, however the extra benefits associated with wound field systems are still essential in modern aircraft.The paper then focuses on the main challenges for improving power density of wound field machines. Recommendations, opportunities and improvements related to wound field machines are discussed. In conclusion, if robust designs for higher speed wound field generators were consolidated, it would be very probable that these classical machines might still be implemented on future MEA platforms.

Electrical machines are required to consistently perform their intended mission over a specified timeframe. The move towards transportation electrification made the electrical machines' reliability an even stringent and predominant requirement, since a failure might cause severe economic losses, as well as, endanger human lives. Traditionally, the design procedure of motors conceived for safety-critical applications mainly relies on over-engineering approaches. However, a paradigm shift is recently taking place and physics of failure approaches / methodologies are employed to meet the reliability figures, while delivering an optimal design. The present work proposes and outlines a reliability-oriented design for low-voltage electrical machines. Thermal accelerated aging tests are preliminarily carried out on custom-built specimens. Once the aging trend of the turn-to-turn insulation system is assessed, the thermal endurance graph at several percentile values is determined and lifetime models are developed, for both constant and variable temperature operations. Finally, these models are used to predict the turn-to-turn insulation lifetime of motors meant for aerospace and automotive applications.

The aviation industry represents an ever-expanding economy and the aircraft market forecast reveals an optimistic growth for the coming decades. New requirements and guidelines call for a more efficient, reliable, and environment friendly aircraft operations during both airborne and ground phases. Considering on-ground operations, the electric taxiing is one of the suggested solutions for reducing the emissions and the acoustic noise in the airport, and for lowering the fuel consumption and the flight costs. This paper provides an overview of the most important existing electric taxiing systems and also presents the basic concepts related to it. Finally, detailed comparison of the different systems is given with recommendations for the future research.

Wound-field synchronous machines (WFSMs) are included in the majority of large power generating units and special high-power motor drives, due to their high efficiency, flexible field excitation and intrinsic flux weakening capability. Moreover, they are employed in a wide range of high-end solutions in the low-to-medium power range. This contribution presents a comprehensive survey of classical and modern methods and technologies for excitation systems (ESs) of WFSMs. The work covers the fundamental theory, typical de-excitation methods and all the modern excitation equipment topologies in detail. It also includes a description of the state-of-the-art and the latest trends in the ESs of wound-field synchronous motors and generators. The purpose of the paper is to provide a useful and up-to-date reference for practitioners and researchers in the field.

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.