This paper describes the main characteristics and the performance of a saturated core type fault current limiter (FCL) rated 45MVA(33 kV-800 A) to be provided by ASG Power Systems. The FCL, which has been submitted to preliminary laboratory testing, will be installed at a 275/33 kV substation in the U.K. and will reduce the fault current by 38%. The device is based on an open geometry of the magnetic cores which allows reduced size and the weight. Magnetic saturation of the cores is obtained by means of two magnesium diboride (MgB2) magnets. A numerical model of the FCL has been developed and validated and the interaction of the device with the power grid has been investigated. Details and results of the model are also discussed in the paper.