Understanding Harmonic Propagation in Meshed Transmission Power Systems with a Large Number of Underground Cables

This outstanding PhD thesis reports on new analytical methods developed to analyse harmonic propagation in large transmission systems. The focus is on understanding the physical relationships between harmonic propagation phenomena in the passive grid caused by grid expansions or changes to existing transmission lines. Principal component analysis and partial least squares regression have been used as tools to investigate statistical correlations between harmonic distortion levels at substations, and a harmonic propagation model based on standing wave phenomena and techniques known from radio and microwave theory has been developed. Knowledge of the propagation phenomena has also been used to develop a new method for determining appropriate locations for harmonic mitigating equipment in a grid. Finally, the methods have been validated through both simulation models and harmonic voltage measurements obtained from the Danish transmission grid. Overall, this thesis reports new insights into harmonic propagation in power systems as the use of underground cables increases and offers new tools for analysing such phenomena. No previous examples of data-driven analyses of measurement data from a power system in the form presented here could be found in existing literature, thus paving a way to new possibilities for this emerging field.