Operational Data for a Large Vertical Thrust Bearing in a Pumped Storage Application©

WILLIAM S. CHAMBERS, (Member, STLE)
ANDREW M. MIKULA, (Member, STLE)
Kingsbury, Inc.
10385 Drummond Road
Philadelphia, PA 19154

This paper presents operating temperatures for a 2756 mm (108.5") 10-shoe thrust bearing installed in a vertical turbine generator in a pumped storage application. The rated output of the generator is 350 MW at a rotational speed of 257 RPM. Temperature data will be presented for shaft speeds up to 257 RPM and loads that ranged from 8.00 to 11.12 MN (1.8 to 2 ½ million pounds) thrust.

The data presented demonstrates the relative effect that the hydrostatic lift has on bearing operating temperatures. Some conclusions are drawn based upon the effect that the hydrostatic lift has on bearing operating temperatures.

Introduction

Fluid film thrust bearings are at risk unless a full hydrodynamic oil film is developed and maintained. This bearing risk condition occurs at starting, stopping and reversing, or whenever the operating speed falls below a certain minimum. When this occurs, full hydrodynamic lubrication is replaced by boundary lubrication, which leads to wear of the bearing babbitt face. One solution to this problem has been the introduction of high pressure oil between the bearing surfaces to establish a hydrostatic lift (high pressure lift).

This paper describes the in-service data collection for a large pivoted shoe or pad vertical thrust bearing equipped with a hydrostatic lift. This particular thrust bearing arrangement is used in each of the six identical pump turbine generators installed at the world's largest pumped storage hydroelectric facility located in Bath County, Virginia. These units are nominally rated at 350 MW generating and 400 MW pumping. Each unit operates at 257 rpm and the dead weight on the thrust bearing is approximately 816000 Kg (1.8 x 10⁶ lbs).

In-service data collection was instituted after several minor wipes of certain thrust bearings had occurred during the commissioning of these units. Investigations resulted in the identification of two problem areas. The first was the discovery of leaks in some of the high pressure lift systems between the check valve and thrust shoes. These leaks prevented the development of hydrodynamic pressure in these shoes and resulted in a corresponding loss of load capacity. The second area identified was a temperature imbalance between the oil bath and feed tube supply systems resulting in thrust shoe radial distortions. The bearings were supplied with an ISO VG 68 lubricant.

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