Polarity Reversal Inhibitor for the Future Meshed HVDC Grids in Presence of DC Circuit Breakers

The development of DC circuit breakers (DCCB) will enable the meshed operation of the future HVDC grids. DCCBs are however expected to cause switching overvoltages and polarity reversal during the fault current interruption process. The attendant higher stresses on dielectric materials, especially on solid insulation systems such as cables, terminations and bushings, could in turn hinder the expansion of existing Voltage Source Converters (VSC) based conventional point-to-point dc links, whose components are not tested for polarity reversal in meshed networks. As a consequence, when evaluating the feasibility of introducing HVDC-DCCBs in existing links, those additional stresses must be carefully assessed, since metal-oxide surge arresters mitigate the overvoltage amplitude but cannot address the polarity reversal phenomenon per se. The paper proposes a device called Polarity Reversal Inhibitor (PRI), which includes both passive and power electronic components, aimed at suppressing the polarity reversal and at the same time reducing the overvoltage amplitude, thus mitigating the stresses caused by the introduction of HVDC breakers into dc links.