Application of Shunt Busbar Capacitor Installations For Protection of VSC-MTDC Grids

High-frequency voltage and current transients due to DC faults are commonly used for designing harmonic-based protection algorithms for multi-terminal VSC-HVDC (MTDC) grids. However, MTDC protection algorithms need high accuracy in discriminating the faulty section for various fault types, with different resistance and locations. This paper studies the principle of adding shunt busbar capacitor installations, which attenuate higher frequency transients of faults outside the protection zone and keep the internal high-frequency fault transients almost unchanged, giving more accurate discrimination between internal and external faults. The impact of the installed shunt capacitors on MTDC dynamic should not be noticeable and the MTDC grid operation should remain normal. A number of indices are defined to evaluate the discrimination accuracy and the injected disturbances caused by different capacitor sizes. The CIGRE DCS2 radial VSC-MTDC system, consisting a combination of overhead lines (OHL) and underground cables has been simulated in PSCAD/EMTDC and further signal processing analysis is done by wavelet and Fourier analysis in MATLAB. Four different fault cases are applied to the system to study the impact of installed shunt filters in different situations.