Power Quality Disturbances in Production Facilities
Examensarbete för kandidatexamen
This thesis is performed for WSP as a part of a longer process to increase WSP’s knowledge of power quality disturbance mitigation in production facilities; mainly wind farms. The different types of power quality disturbances are defined and their causes and effects explained. A wide range of available devices which can be used to mitigate these disturbances are reviewed. The basics of wind power are also explained briefly, including a review of different turbine types. The broad range variable-speed turbine types – where the turbine is controlled through a frequency converter – are today very dominant. The central part of the thesis describes how disturbances are handled in wind farms. Mainly, flicker and harmonics have to be considered, but also unbalance, rapid voltage changes, voltage dips, transient overvoltages and frequency variations. Flicker severity is subjective and therefore flicker is difficult to quantify. However, flicker seldom requires special mitigation in new wind farms. Harmonics are the main problem and are eliminated with passive filters, primarily placed inside of the turbines, at the converters. Also, amplification of existing harmonics due to resonance effects needs to be considered. General allowed levels in the power system for each disturbance type are presented. Allowed emission levels for a specific wind farm are set by the network owner after calculations of the power system impedance have been performed. A computer-based tool for choosing mitigation devices was originally planned to be designed in this thesis, but this idea was abandoned when it became clear that only filters are used in practice and that their properties are proprietary information. Lastly, some possible future developments of wind power and the power system which could affect disturbance mitigation are discussed.
Elkraftteknik , Electric power engineering