A 0.3 MJ SMES magnet of a voltage sag compensation system

To protect an 110 kVA critical load from voltage sags, a SMES-based voltage sag compensator is developed. This system consists of a 0.3 MJ NbTi magnet and a 150 kVA IGBT-based current source converter. The magnet has a solenoidal coil with an inductance of 1.85 H. Its helium-vapor cooled HTS current leads are further cooled by liquid nitrogen. A protection system is designed for quenches which would most likely happen during the period of charging or discharging of the magnet when a voltage sag occurs or the voltage supply recovers from a sag. The topology of the main circuit of the compensator is also presented and analyzed.