Transmission line protection performance in presence of power electronic-interfaced devices : Impact and needed countermeasures in the Swedish transmission system

Abstract: The penetration level of power electronic-interfaced devices (PEID:s) in power systems isincreasing, including wind- and solar power, HVDC and FACTS devices. Fault current injectedby PEID:s is lower in magnitude, may lack or contain a reduced negative sequence componentand can have a wide range of phase angles, as opposed to fault current supplied bysynchronous generators (SG:s). In this thesis, the impact of these changes on transmission lineprotection in the Swedish 400 kV network is investigated trough a literature review and steadystate short circuit simulations.The literature review shows that residual overcurrent protection and line differential protectionworks well in presence of PEID:s in most cases. Traveling wave based protection and other fasttime-domain protection may be suitable as well. Some type of distance protection on the otherhand, are facing challenges associated with their impedance, directional and fault identificationalgorithms, when PEID:s are the only fault current source. This is partly caused by varying prefault grid conditions, lack of negative sequent current and oscillations in fault current magnitudeand phase angle caused by the PEID controller. The thesis underlines the need for anincreased understanding of specific algorithms included in distance protection in the Swedish400 kV transmission system, as their performance in presence of PEID:s likely varies betweendifferent vendors and year of manufacturing.