Scan M DeCamillo1 Peter J. Clayton2
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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