The study examines hydroelectric power generator characteristics, voltage quality, air gap and vibration, in different operational modes -no-load mode, 90, 45, 10 MW load, 90 MW load with −50 MVAr to 20 MVAr reactive power and synchronous compensator mode with 0 MW-20 MW active power and synchronous compensator mode with −10 MVAr to −60 MVAr reactive power.Developed framework for power quality and air gap measurements assessment of hydropower generator shows that correlation exists between voltage, air gap and vibration characteristics. Analysis and comparison of different operational modes are performed to identify, which modes are important during diagnostics of machine condition in hydroelectric generators.