Impact of DFT-Based phasor estimation errors due to commutation failures of LCC-HVDC links on the protection of AC lines in the near vicinity.

• Commutation failures on LCC-HVDC systems cause distortion on voltage and current waveforms of nearby AC system, leading to phasor estimation errors. • Half-cycle algorithms suffer more from inaccuracies than full-cycle ones when quite distorted signals are evaluated, revealing the use of short windows may be an issue for protection schemes in these scenarios. • Zone 1 of distance relays may misoperate, overreaching close-in externals faults. To overcome this drawback, the zone 1 reach can be reduced, or it can be deactivation as a more conservative approach. • Both phase and sequence line differential elements operate correctly, even during commutation failure of LCC-HVDC systems, preventing false trip command issuing for external faults. • Directional overcurrent element operated correctly most of time. However, zero and negative sequence elements may misoperate for phase-to-phase and three-phase faults. Therefore, it is recommend not choosing small pick-up values for this function. Commutation failure (CF) is an inherent issue for Line-Commutated Converter (LCC) HVDC technology. Whenever it happens, voltage and current waveforms throughout the AC system in the near vicinity of LCC-HVDC links become quite distorted. In this paper, it is assessed the impact of such kind of distortion on transient response of phasor estimation algorithms and, in turn, on the performance of AC transmission lines protection. Different discrete Fourier transform (DFT) based algorithms are implemented, and distance, differential and directional protection functions are evaluated. The obtained results reveal that phasor estimation errors arise whenever CFs take place, which may lead protection functions to misoperate, such that false trip command may be issued for external faults. [ABSTRACT FROM AUTHOR]