Electromagnetic Analysis of Hydroelectric Generators

• Main Author: Ranlöf, Martin
• Format: Doctoral Thesis
• Language: English
• Published: Uppsala universitet, Elektricitetslära 2011
• Subjects: Contra-rotating rotors; damping torque; damper winding; finite element method; hydroelectric generators; permeance model; pole shoe shape; rotational losses; single machine infinite bus; slot ripple; synchronizing torque; synchronous machines; voltage waveform.; Engineering physics; Teknisk fysik
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-146629; http://nbn-resolving.de/urn:isbn:978-91-554-8027-1

Hydropower maintains its position as the most important source of renewable electric energy in the world. The efficiency of large hydropower plants is unsurpassed, and after more than hundred years of development, the technology is mature and highly reliable. While new hydro resources are currently being developed in Asia and South America, most European countries go through a phase of intense refurbishment and upgrading of existing plants. Challenges faced by the hydropower industry include a knowledge transfer to new generations and the adaptation of unit designs to meet new operational requirements. As with all branches of engineering, the use of computerized design tools has revolutionized the art of hydropower plant design and the analysis of its performance. In the present work, modern tools like coupled field-circuit models and semi-analytic permeance models are used to address different aspects of electromagnetic analysis of generators in large hydropower plants. The results include the presentation of a mathematical model that uses concepts from rotating field theory to determine the air-gap flux density waveform in a hydroelectric generator. The model was succesfully used to evaluate armature voltage harmonics and damper bar currents at no-load and load conditions. A second study is concerned with the importance of losses due to rotational fields in core loss calculations. It is found that dynamic and rotational effects typically increase the total core loss estimates with about 28% in large hydroelectric generators. In a third study, linear models for the calculation of salient pole shoe form factors at an arbitrary level of magnetic loading are presented. The effect of the damper winding configuration on the damping capability of salient-pole generators is then evaluated in a separate study. The predicted impact of the coupling between damper cages on adjacent poles on the damping torque production is verified in a set of experiments.