Electric Contact Material Selection for Medium and High Voltage DC Circuit Breakers

Medium and high voltage DC grids are increasingly proposed for terrestrial, shipboard and aircraft power systems. However, multi terminal DC networks can only be realized with the development of a DC circuit breaker. Due to the difficulty in breaking DC currents, hybrid circuit breakers-which consist of a non-arcing fast mechanical disconnect switch (FMS) in parallel with a solid state switch-is the most promising solution. The stresses experienced by the electric contacts of FMS are different from those of AC and low voltage DC breakers and disconnect switches. The choice of contact material has a significant impact on the performance of the DC circuit breaker. The Ashby method is used to systematically identify the best suited contact materials by translating the requirements of FMS contacts into objectives and constraints and deriving material indices for each objective. Minimizing power loss, wear and overheating of contacts are identified as the key objectives. The results suggest that copper-based alloys and compounds are more suitable than silver based alloys and compounds and other contact materials.