Performance Tests of an I8-Inch Diameter, Leading Edge Groove Pivoted Shoe Journal Bearing

Scan M DeCamillo¹ Peter J. Clayton^2
1Kingsbury, Inc., 10385 Drummond Road, Philadelphia, PA, 19154, U.S.A.
²Westinghouse Power Generation, The Quadrangle, 4400 Alafaya Trail, Orlando, FL, 32826, U.S.A.

This article presents results from performance tests of 457 / mm (I8-inch) diameter LEG pivoted shoe journal bearings supporting a 470 MV A generator rotor. Leading Edge Groove (LEG) is a method of lubrication that delivers cool oil directly into the oil film to increase bearing efficiency and has been successfully implemented in thrust bearings for more than ten years. Small LEG journal bearings have more recently been applied with favorable results. However, prior to this report, benefits for much larger journal bearings have been only projected. The test data presented in this article confirms prior projections: i.e., significant reductions in power loss were obtained, lubrication requirements were reduced by up to 46 percent, and low bearing temperatures were maintained. Performance and dynamic test data are presented which show that the application of leading edge groove lubrication to pivoted pad journal bearings can reduce lubrication system size requirements and significantly improve rotating machinery efficiency.

Introduction

The demand for energy in Asian countries is rapidly increasing and dynamic growth has focused on gas turbine combined cycle technology, attributed to the increased efficiency of such systems [1]. Predictions state that over a third of the generating capacity in Great Britain will be gas fired combined cycle plants by the end of the century. This trend is attributed to Privatization which makes these low cost/high efficiency systems attractive [2]. In the USA, expansion is slower and the outcome of deregulation is uncertain. Even so, the economics of competition suggests that companies witll the lowest generating costs will be more successful [3]. Original equipment manufacturer competition has also established trends for low cost, high efficiency units with longer durations between maintenance outages.

Machine efficiency is degraded by power loss in the bearings. Bearing losses greatly increase with surface velocity and become especially high in large power generating units. In 1981, the British Institute of Petroleum published a report that addressed losses in turbo generators [4], indicating that a 15 to 20 percent reduction in bearing losses in the United Kingdom's power generation equipment would contribute to savings on the order of$50 M per year.

Leading Edge Groove (LEG) technology is a method of bearing lubrication that addresses the reduction of bearing power loss. With this method, cool oil is delivered directly into the oil film of each pad. Tests of small (l02 / mm), high speed journal bearings have obtained oil flow reductions of 50 percent and power loss reductions of 26 percent using LEG lubrication, while maintaining low pad temperatures as compared to flooded bearing designs. From these results, significant advantages were projected for large machines, not only in improved efficiency, but in savings possible with smaller, more efficient bearing lubrication and cooling systems [5].

With such background, the authors teamed to develop and test an LEG design journal bearing for a large electric generator application. The main objectives were to manufacture a cost effective bearing design that decreased bearing oil flow requirements and power losses, and to test the production size bearing to assure it would operate with acceptable pad temperatures and rotordynamic response. The following sections report on the results of this work.

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