Impact of VSC converters fault current injection on Incremental Quantities based distance protections

Renewable energy sources (RES) and high-voltage direct current (HVDC) links are interfaced to the grid using power electronic converters (PECs). Unlike traditional synchronous generators, PECs fault behaviour is fully controlled and needs to satisfy grid code requirements. This regulated fault current behaviour presents significant challenges to protection schemes. Incremental Quantities (IQ) line protections are a type of time domain protections. These protections are advantageous because they can respond to faults more quickly than traditional phasor-based distance protections. Faster fault clearing enhances system stability and reliability and improves power quality. An example of such a protection scheme is the TD21 distance protection element, implemented in the commercial SEL-T400L relay. The objective of this thesis is to analyse the impact of fault current injection by voltage source converters (VSCs) on the TD21 distance protection element. To achieve this, several tasks were undertaken: a literature review on the fault behaviour of PECs, the implementation of a VSC model in MATLAB/Simulink, a review of incremental quantities-based protections, and the implementation of the TD21 element in MATLAB/Simulink. Simulation results reveal that the VSC's fault current affects the performance of the TD21 distance protection element. The reduced fault current provided by the VSC can hinder the protection element's ability to detect in-zone faults effectively. Additionally, the irregular fault current during the VSC's transient response can lead to incorrect operation of the protection element for faults outside the protected zone.