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 paper provides the data collected over a three-year period to illustrate the dynamic air gap change depending on generation modes of four hydropower generators with similar design. The tests were performed on hydropower units at the rated apparent power of 105 MVA and the air gap of 20 mm. The results obtained showed that the average air gap change in different modes could reach up to 2.1 mm. Around 90 % of air gap change results from thermal expansion and 10 % were determined by centrifugal and magnetic forces. In coasting mode when the power was switched off and the speed of the generator decreased, the air gap increased up to 0.7 mm. Attraction forces resulting from magnetic phenomena accounted for 0.1-0.6 mm decrease in the air gap.
The paper is devoted to vibration of the foundations for rotary screw compressors used for gas compression for thermo power plant installed on skid mounting. To evaluate the compressor vibration according to the industry standard VDI 3836, the user should decide whether the foundation is rigid or resilient. The foundation is rigid, if the vertical natural frequency of the foundation is at least 25 % higher than the excitation frequency. The excitation frequency, compressor running speed in Hz is normally known, while the natural frequency is usually not known. Therefore the goal of the study was to find natural frequencies of the skid using analytical calculations, SolidWorks simulation and "bump testing" on site. In the results section it is shown that vibration in axial direction is usually higher for screw compressors than in radial direction, therefore the mathematical model with compressor shaking horizontally was adopted for this study. Limitations of the bump test were discovered. The examples of distinctive and indistinctive spectrum were presented. It was concluded that for the structure of screw compressor foundation the bump testing on site is rather an ineffective tool to detect natural frequencies, because there are too many frequencies appearing in the spectrum and no natural frequencies could be distinguished from the time waveform. Therefore, testing of the equipment foundation natural frequencies has to be performed in the manufacturing facility before installing the equipment and filling the frame with concrete.
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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