This paper studies, using experimentally verified Finite Element analysis, various performance measures of the Brushless Doubly Fed Induction Generator (BDFIG) when magnetic wedges are used for closing stator open slots. The BDFIG is an attractive generator solution for offshore wind power and can replace doubly-fed slip-ring induction generators. It is shown in this paper that the use of magnetic wedges, commonly used in large induction machines, reduces the stator windings magnetising currents in a BDFIG, reflected in the values of magnetising inductances. They also increase the leakage flux in the stator slots, leading to a larger series inductance in the equivalent circuit. The series inductance significantly affects the BDFIG performance as well as the rating of its converter. The effects of magnetic wedges on BDFIG air gap flux, synchronoustorque and stator tooth top saturation is also investigated. 2-D finite element analysis of an experimental 250 kW BDFIG is used in the study, verified by experimental measurements.