Experimental investigation of large spring-supported thrust bearings used in hydroelectric generators

Abstract

Large spring-supported thrust berings are key components in hydroelectric generators and have not been considered in much detail in the academic literature. The present thesis describes the application of a comprehensive commercial software package (GENMAT) to provide numerical predictions of spring-supported thrust bearing performance. A minor study of the accuracy of the pad deflection model in the software package was performed with a finite element analysis but the issues of accuracy were not resolved. GE Hydro's unique test facility for large thrust bearings was commissioned and extensive experimental measurements of film thickness, pad temperatures and film pressures were collected and compared with numerical predictions of GENMAT.

The agreement was good for the temperatures and the shape of the pad but somewhat erratic for film thickness and poor for pressures. The film thicknesses had been measured with effy current displacement probes and their output voltage relationships to target distance, temperature, pressure and target material were characterized in subsequent laboratory experiments. Although probe calibration was implicated in the accuracy of the film thickness measurements, other unknown factors also contributed. An argument was made for accepting GENMAT predictions of film thickness for a given case, provided the temperatures and pad shapes showed good agreement. The neglect of rotor crowning was suggested as an explanation for the poor agreement of the pressures.

A combination of theoretical and experimental investigation was performed on a large number of cases. It was found that minimum film thicknesses were always about 15-20 um despite considerable variation in geometry, lubricant viscosity, loads and rotor speeds. Temperature was influenced more readily by these variations, thus suggesting that energy efficiency which depended to a large extent on lubricant temperatures could be improved while maintaining adequate film thickness. Recommendations were made for more extensive application of the GENMAT package to the design of better spring-supported thrust bearings.