Optimal Shunt Busbar Capacitor Placement for Selective Protection of Large-Scale VSC-MTDC Grids

Abstract

This paper studies optimal shunt busbar capacitor placement for large-scale VSC-MTDC grids to accurately discriminate between faults inside each protection zone and external faults. The installed capacitors work as filters, which attenuate higher frequencies for faults outside the zone and keep internal fault transients unchanged. The objective function is a trade-off between total installation and maintenance cost and the discrimination sufficiency, while constraints related to the grid operation must be satisfied. Discrete wavelet transform (DWT) is used to calculate wavelet energies and to define relay detection criteria. The proposed method is applied to CIGRE large-scale VSC-MTDC grid in PSCAD/EMTDC. MATLAB is used for DWT-based signal processing with Python used as an interface between PSCAD and MATLAB for optimization based on the Watercycle optimization algorithm (WCA). Multiple faults with different characteristics are simulated to test the optimal results in different situations. The optimal results show that the proposed principle accurately discriminates between internal and external faults. Simulation results prove accurate detection of the faulty section using both two-sided measurement and one-sided measurement with half of measuring and protection equipment. The sensitivity of the method to faults close to the measuring points and the impact of different DWT levels is analysed.