This paper deals with basic performance of a design of a two-pole three-phase 40 MVA synchronous generator designed for special operating conditions in laboratory for testing high power transformers. The generator is designed to test three-phase and single-phase transformers aimed to work within 50 Hz and 60 Hz network frequency. This means that the generator will operate at two nominal speeds, at 3000 rpm and 3600 rpm, with nominal power of 40 MVAr induction load when rating with symmetrical three-phase load. The additional requirements relate to constant operation with two-phase 25 MVA load and single-phase 13.5 MVA load, since for testing single-phase and special transformers phase connection you like will be used. In the course of designing, special attention was paid to correct dimensioning of the damper rotor winding as well as to the geometry of stator windings, rotor and air gap, which in the end will produce minimum voltage wave distortion, i. e. generator voltage wave shape with harmonious content less than 1% (as it was demanded).