Analysis of High-Frequency Electrical Transients in Offshore Wind Parks

Licentiate thesis, 2009

In this thesis, a study of high frequency electromagnetic transient phenomena is performed. Models of various components needed for simulations of high frequency transients, such as transformers, cables and breakers are developed. Also, measurements of high frequency transients are performed in the cable laboratory in ABB Corporate Research in Västerås, Sweden for the purpose of parameter estimation of models and for verification of simulations. Some critical cases where the voltage surges of the magnitude and/or rise time above basic lightning impulse voltage level appear, are identified. Also, some transient protection schemes are analyzed and the performance of different transient mitigation devices is studied. Furthermore, the energizing transient of the Utgrunden wind park is analyzed and the simulation model is verified using the measurements. The energizing transient simulation predicted accurately the magnitude and the frequency of the transient voltages and currents. Simulations of the high frequency transients are in a very good agreement with the measurements obtained in the cable lab. Simulations predicted accurately critical surges with the highest magnitude and matched with good accuracy surge waveform recorded during the measurements. During the testing and simulations, surges which exceed the basic lightning impulse voltage level of dry-type transformers specified by IEEE standards, both in magnitude and rise time are observed even when surge arresters are used. It is confirmed both in simulations and measurements that use of additional transient protections devices such as surge capacitors and RC protection, decreased the magnitude of surges below the critical level.