Impact of Protection Devices on the Unavailability Risk of Low-Voltage Direct Current Systems

Many options are available when it comes to protecting low voltage direct current grids. As each type of protection device has different tripping characteristics, they all have their own unavailability risk, which is the cost of unavailability. This paper proposes a method that uses transition frequency densities to determine the unavailability risk. These transition frequency densities are determined through a semi-Markov process and are used to calculate the unavailability risk of a simple use case as presented in a numerical illustration. Fuses are the most cost-effective type of protection device for the presented numerical illustration, however, cannot be used under all circumstances. Solid state circuit breakers are to be used in highly critical systems, mechanical circuit breakers when the cost of outage is relatively low and hybrid circuit breakers in between.