Determination of DC Short-Circuit Currents of MMC-HVDC Converters for DC Circuit Breaker Dimensioning

At a short circuit in an HVDC system modular multi-level converters with half-bridge submodules contribute to the short-circuit current even after blocking of the submodules. DC circuit breakers are therefore necessary for the interruption of the short-circuit current especially for the reliable operation of multi-terminal HVDC systems. In this paper a calculation method of important parameters of the short-circuit current is presented. The DC short-circuit current is determined by the characteristics of the AC and DC system. The substantial influence factors are evaluated and based on the ratings of existing VSC-HVDC projects typical AC and DC impedances are derived. For different HVDC scenarios resulting short-circuit currents are calculated. The paper concludes with recommendations for the calculation of short-circuit currents in radial and meshed HVDC grids.