A Pilot Protection for Flexible Low-Frequency Transmission Line in Offshore Windfarms Based on Fault Multi-Band Calculated Energy

In offshore wind power systems with flexible low-frequency transmission line, fault responses present weak feed characteristics from both sides, resulting in limited fault current magnitude and controlled phase angles. Traditional pilot protection schemes face risks of non-operation or mis-operation. Additionally, reduced power frequency may lead to a serious decrease in the rapidity of pilot protection. To address these challenges, a novel pilot protection based on fault multi-band calculated energy is proposed. The paper first analyzes the fault characteristics of the flexible low-frequency transmission line. Transient power contains abundant fault information, with significant differences in bilateral power disparities across multiple frequency bands between internal and external faults. Secondly, based on these characteristics, wavelet transform is employed to decompose normalized signals across multiple frequency bands, followed by weighted energy calculations for each frequency band. Finally, a protection scheme based on fault multi-band calculated energy ratio is established. The proposed protection scheme is validated through simulation models on the PSCAD/EMTDC platform, the result shows that the proposed scheme can accurately distinguish internal/external faults and fault phases, while maintaining considerable resistance to transition resistance.