A Superconducting Magnetic Store for Grid Frequency Support: Coil Inductance, Conductor Mass, Cryogenic Load and Millisecond Response for One Usable Kilowatt-Hour

This paper sizes a superconducting magnetic storage system for a transmission substation requiring instantaneous power injection to arrest frequency excursions. The duty calls for 1 usable electrical kilowatt-hours delivered at a rated power of 1e+03 kilowatts. Working from a stated specific energy of 7 watt-hours per kilogram, an energy density of 12 watt-hours per litre, a usable depth-of-discharge fraction of 0.9, and a round-trip efficiency of 95 percent, the calculation gives a gross stored energy of 1.11 kilowatt-hours, an active-store mass of 159 kilograms, a complete system mass of 317 kilograms, and a complete system volume of 185 litres (0.185 cubic metres). Full discharge at rated power lasts 0.001 hours, and a full recharge takes 0.0011 hours at the stated charge power. Losses amount to 0.057 kilowatt-hours per complete cycle, appearing as heat at average rates of 25 kilowatts during charging and 28.5 kilowatts during discharge. Standing loss is 0.5 percent of the stored energy per day. Life is limited by the calendar limit, giving 7.5e+03 effective full cycles, about 25 years at the assumed cycling rate, and a lifetime delivered throughput of 7.5 megawatt-hours. All values are computed from the stated assumptions; the system is a design study and has not been built or measured. Status: SIMULATED, NOT MEASURED.