Inverse time overcurrent protection scheme for fault location in multi-terminal HVDC

One of the main challenges with HVDC multi-terminal (MTDC) configurations, which are based on voltage source converters (VSC), is the protection system. The dc grids have small series inductances which made them unable to limit the rise time of the DC current when a dc fault occurs. For this reason, the dc fault clearing must be performed very fast in order to limit the effect of the rapid increase of the dc current during dc faults. However, before clearing the line, the fault must be detected and located as soon as possible. The fault location is very challenging using conventional methods that have been used in ac system. This paper investigates a fault location algorithm based on inverse-time overcurrent characteristic. In this algorithm the protection operating time is inversely changed with the current magnitude, so in order to implement it, feed inductor at each cable terminal is needed. A simplified version of CIGRE B4 DC Grid Test System is implemented in PSCAD to test the proposed algorithm.