Analysis of DC breaker requirements for different HVDC grid protection schemes

This paper compares the DC breaker requirements for different DC breaker protection schemes for high voltage direct current (HVDC) grids with half bridge converters. DC breakers are essential for DC grid protection as they can provide a selective and fast protection. The DC breakers experience challenging operation conditions which results in an increased cost to meet the breaker requirements. The breaker requirements are strongly determined by the employed protection system. As such, the solution of breaker and protection system is strongly linked. A solution to reduce the requirements is by choosing the best suited protection method concerning the breaker requirements. In this paper, two proposed protection methods and their breaker requirement are explained and compared. The first protection method is a full selective DC protection (FSP) similar to AC protection. A second option, referred to as open grid protection (OGP), is by opening each breaker independently in case of a fault. The reduction potential of the dissipated energy requirement of the DC breaker of both protection schemes is simulated by applying a pole-to-ground DC fault in a four-terminal network with modular multi-level converters. The required energy for the different protection schemes is investigated for different current ratings and switching times. All studies have been performed using PSCAD/EMTDC. From the advantages and drawbacks of these two protection schemes, a new protection method is proposed.