The brushless doubly-fed reluctance generator (BDFRG) is an excellent candidate for renewable energy applications such as wind turbine generators. It requires a converter with only a fractional rating to operate over a designated speed range and thus the cost of the power electronics can be reduced. This paper discusses a grid-connected BDFRG and the effects of varying the machine dimensions on the performance. If the machine is too small then it may suffer from saturation problems leading to low efficiency and also the reluctance ratio in the rotor may be poor. This means that the BDFRG may not be suitable for generating systems under a certain power rating. A power generation estimation process (PEP) for the control and power windings of the BDFRG is introduced. The proposed PEP is capable of calculating and determining: (a) the grid voltage; (b) the alignment between the rotor position and current excitation and (c) the appropriate voltage phase difference between the control and grid windings. Two scaled designs are compared and dimensioning effects are demonstrated. Finally, an experimental study is carried out to verify the simulation.