Comparison of availability between 4.2 K and 77 K SMES concepts

The influence of nitrogen cooled superconductors on the availability of a 100 kWh SMES concept has been analysed. A conceptual design of a reference unit at 4.2 K has been used as a basis of the study. This kind of unit, with independent control of real and reactive power, is suitable for load management-for example in foundries. A comparison of availability has been performed between the 77 K and 4.2 K concepts. In order to perform this analysis, one has to assume that the mechanical and electrical performance of an HTSC cable is equivalent to that of a conventional one. The method used is based on failure modes, effects and criticality analysis (FMECA). Fault trees describe the outage logic based on the functional analysis. Event trees clarify the consequences of the primary events and the criticality of these consequences is expressed as a system downtime. The existing database is very limited, so extrapolation of data from other technologies cannot be avoided.