PURPOSE: To prevent the occurrence of disturbance to a power system due to running of a vehicle by a method wherein an SMES (superconduction energy storage device) is mounted in the vicinity of each substation, the SMES is connected to a power system through two or more converters, and a fluctuation in a tidal current from a generator is minimized.

CONSTITUTION: In a device which feeds a power generated by a power station 1 to stringings 8 and 9 through a transformer 7 in each substation, SMESes (SMES S1 - SMES Sn) are set in the vicinity of a substation, a power equivalent to fluctuation in a feed power occasioned by running of a vehicle is fed from the SMES, and the feed of a power is always maintained at a specified value P0. Each SMES is formed with a superconduction coil 2, converters 3 and 4, a transformer 5, and a control device 6. When a power on the system side is transferred to the SMES side, an exciting amount of the superconduction coil 2 is increased by means of a current power-rectified to a DC through the transformer 5 and the converters 3 and 4, and a power stored in the SMES causes power-inversion of the converters 3 and 4, and excited energy of the superconduction coil 2 is transferred to the system side.