PERFORMANCE AND RESILIENCE OF A SPRING-SUPPORTED THRUST BEARING OF A HYDROPOWER UNIT

Abstract

This paper describes a study of the performance of a spring-supported thrust bearing used in a 339-MW hydropower unit. The spring pattern had been optimized in the past by removing six springs under the leading edge of each pad to reduce maximum babbitt temperature. Detailed simulations performed in this investigation, however, revealed that performance gains were not consistently apparent beyond a certain temperature threshold in normal operation. Furthermore, one critical finding of the study was that because the pads are relatively thin, pad and babbitt undergo a bowl-shaped deformation at zero speed in hydrostatic mode, to the point that film thickness at the corners of the pad becomes an issue during maintenance operations. This difficulty in forming a thick enough oil film under hydrostatic conditions is exacerbated with the optimized spring pattern, which shifts the maximum pressure zone away from the center of gravity of the springs. An alternative is thus proposed to address this issue: a modified preload of the six inlet springs. The study results show this alternative combines most of the advantages of the optimized spring pattern in the hydrodynamic regime and of the original spring pattern in the hydrostatic regime.

Bearing performance was also investigated under adverse conditions: presence of two scratches on the babbitt surface. Simulations revealed that a circumferential scratch near the center of the pad cut the zone of maximum pressure into two parts, reduced load-carrying capacity and diminished the oil film by 10 to 20%. A scratch of this type is also a concern in the hydrostatic regime. An off-center scratch, on the other hand, seemed to have only a minor impact on bearing performance. We also studied the possibility of scraping the babbitt surface to remove the scratches. Our findings suggest that reducing the thickness of the babbitt does not compromise bearing performance in normal operation, offering an approach that can effectively address surface scratches and wear concerns.