The extended testing of hydrogenerator (rated 35 MVA) was made because the generators working age expired and it was going to be replaced with new one. This was the perfect opportunity to do some specific and not usual testing. The complicated testing plan was designed in order to enable recording as much relevant data as possible (electrical, electromechanical, mechanical). Therefore in some phases of testing, 29 to 44 quantities were measured simultaneously. Further, the results of measuring and simulation for asynchronous operation of synchronous generator are shown.