Protection of VSC-HVDC systems with mixed usage of power cables and overhead lines
Aachen / Verlagshaus Mainz (2020) [Book, Dissertation / PhD Thesis]
Page(s): 1 Online-Ressource (viii, 118 Seiten) : Illustrationen, Diagramme
The integration of VSC-HVDC transmission systems into existing AC grid structures is identified as a key solution to increase the accessibility of remotely located renewable generation. At the same time, realising new transmission corridors is often confronted by public objection. In an effort to reduce planning and commissioning processes, transmission systems with mixed usage of power cables and overhead lines are expected to assume an increasingly important role in the future transmission grid. However, several technical challenges still have to be addressed, in particular the reliable, fast and selective handling of line faults. Since line protection concepts proposed for VSC-HVDC systems today typically only account for either pure cable or pure overhead line transmission, a comprehensive investigation of the transient fault behaviour in mixed systems is needed to be able to assess and further develop the existing methods. In this work, topological impact factors on the voltage and current characteristics are analysed based on electromagnetic transient simulations in the time domain. As a result of travelling wave reflection and transmission effects, which occur at every transition point between a cable and an overhead line section, the initial fault impacts at the transmission line ends and segment interfaces can vary significantly depending on the line topology and the fault location. On the one hand, amplified wave fronts can cause increased voltage and current stresses compared to pure cable or overhead line systems. On the other hand, the initial fault effects at the line terminations can be attenuated significantly without a clear indication of travelling wave fronts. Since most of the proposed fault detection and localisation methods rely on an identification of steep voltage and current changes, comprehensive line protection is no longer guaranteed. To address these challenges, distributed voltage and current measurements are introduced at the line transition points as well as end-to-end and interface-to-end communication channels to transmit the measurement data to the line ends. On this foundation, additional voltage-based detection criteria and a rate-of-change-of-current-based localisation algorithm are incorporated into the protection concept, along with further enhancements, e.g. for applications in multi-terminal DC systems. The functionality and flexible applicability of the developed methods is validated in exemplary test systems pointing out the successful detection, separation and localisation of faults in all of the investigated scenarios.
Tünnerhoff, Philipp Christian