Use of fast circuit breakers to mitigate overvoltages in VSC HVDC point-to-point schemes

Sustained DC-side overvoltages in HVDC point-to-point schemes may occur on the healthy pole when DC-side pole-to-ground faults occur. Until now, the impact of these DC-side overvoltages on cable systems is not well known. Several mitigation methods have been proposed until now, including actively switched DC- or AC-side surge arresters. This paper investigates the potential of using fast AC-side or DC-side circuit breakers for mitigating DC-side overvoltages using EMT analysis. To reduce peak overvoltages, any AC- or DC-side circuit breaker solution must be sufficiently fast acting, even though all investigated solutions show limited potential. All investigated solutions show that sustained overvoltages can be mitigated, thereby reducing DC-side surge arrester requirements at a limited energy absorption requirements of the AC- or DC-side circuit breaker. The simulation-based study should be complemented with investigations towards the practical realization of such solutions. • In symmetrical monopolar schemes, overvoltages may appear during DC-side pole-to-ground faults. • Fast circuit breakers at AC or DC side can mitigate these DC-side overvoltages, especially with respect to the duration. • In all studied EMT cases, the burden on the pole arresters is heavily reduced at only a moderate breaker arrester energy.