ABSTRACT
The use of the classical, wound-field synchronous generator in the field of power generation, as opposed to a permanent magnet machine, is driven by the need of controlling the field winding voltage and current in such a way to guarantee a constant voltage at the generator’s armature terminals. In a traditional generating set, this function is accomplished by a relatively complex feedback control system which tipically comprises an excitation system and an automatic voltage regulator. Due to their excellent and proven performance capability, such classical generating sets have seen only strictly incremental improvements in the last 60 years or so. However, today, there is an interest in revamping their design and development, partly due to the ever increasing efficiency and reliability requirements and partly due to advances in materials and manufacturing techniques.
This thesis investigates the feasibility of a hybrid permanent magnet - field winding excitation for the exciters of synchronous generators. This design solution aims at improving the efficiency of the whole gen-sets, while also increasing the reliability of the overall system. As vessel for studying the proposed concept, the exciter of an alternator in the power range of 400kVA is investigated. Advanced analytical and finite-element models are first implemented and then validated against experimental results. The validated tools are then used to achieve optimal design solutions, whose performance are finally compared to the original exciter design.
