Analytic Approximation of Fault Current Contributions From Capacitive Components in HVDC Cable Networks

A novel approach for the calculation of transient fault current contributions from capacitive network components in HVDC cable networks during pole-to-ground faults is presented in this paper. Analytic approximations considering the skin effect and the resulting distortion of the waveshape of the fault surge are proposed. Only fault current contributions from capacitive components, such as dc capacitors and adjacent cable feeders, are taken into account in this paper, since they are dominant during the first few milliseconds and yield the highest rates of rise of fault current. The results of the proposed expressions are compared with a benchmark model implemented in PSCAD and exhibit an accurate representation of the time development of the fault current. The derived approximations may serve as a starting point for a short-circuit calculation standard for HVDC networks and the specification of HVDC circuit-breaker requirements.