Utilization of cable capacitance in GTO-HVDC transmission

The voltage-source, GTO-HVdc stations require capacitor banks at their dc terminals for two purposes: (i) filtering of the GTO switching noise and {(ii) voltage support. This paper examines the feasibility of exploiting the capacitance of submarine andlor underground cables, thus offsetting some of the cost. It is shown that the capacitance of cable length as short as 10 km can significantly reduce the Total Harmonic Distortion (THD) of the dc voltage from 7.76% to 2.26%. However, the THD of the dc current is of the order of 18%. An inductor of 20mH (0.106 P.u.) is sufficient to reduce the current THD to 7%. The cable is modeled as L-R-C n section representation of the transmission line (1-section per km). The results are obtained by digital simulations (Matlab/Simulink).