Design optimization of a permanent-magnet saturated-core fault-current limiter

Designs of saturated-cores fault current limiters (FCLs) usually implement conducting or superconducting DC coils serving to saturate the magnetic cores during nominal grid performance. The use of coils adds significantly to the operational cost of the system, consuming energy, and requiring maintenance. A derivative of the saturated-cores FCL is a design implementing permanent magnets as an alternative to the DC coils, eliminating practically all maintenance due to its entirely passive components. There are, however, various challenges such as the need to reach deep saturation with the currently available permanent magnets as well as the complications involved in the assembly process due to very powerful magnetic forces between the magnets and the cores. This paper presents several concepts, achieved by extensive magnetic simulations and verified experimentally, that help in maximizing the core saturation of the PMFCL (Permanent Magnet FCL), including optimization of the permanent magnet to core surface ratios and asymmetrical placement of the permanent magnets, both creating an increase in the cores' magnetic flux at crucial points. In addition, we point to the importance of splitting the AC coils to leave the center core point exposed to best utilize their variable inductance parameters. This paper also describes the stages of design and assembly of a laboratory-scale single phase prototype model with the proposed PMFCL design recommendations, as well as an analysis of real-time results obtained while connecting this prototype to a 220 V grid during nominal and fault states.