The air gap monitoring and fault diagnosis is exemplified for a slowspeed salient-pole generator of hydropower unit. Three types of measurements, namely, with contacting probes, non-contacting sensors and non-invasive sensors are discussed. For the case study non-contacting sensors were applied, with the results demonstrated. In the paper, different methods for evaluation of the results (e.g. using delta value and air gap variation criteria, graphical and spectrum analysis) are described and compared. It has been shown that the spectrum analysis describes changes in the eccentricity better than the criterion method, and is expected to supplement the graphical analysis in the future. Finally, the limitations of the spectrum analysis are formulated, and criteria for this type analysis are proposed.

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.

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