The increasing introduction of intermittent power sources combined with the
de-regulation of electricity markets has led to increased instability in the electrical
grid. This has led to increased start-up and shutdown of regulating power
sources such as hydro-electric power plants and operation at non-ideal operating
states both of which increase the wear and tear on machines. Likewise, the
push for a less environmentally intrusive society has raised the importance of
utilizing equipment with reduced impact on the natural surroundings.
These challenges lead to a need to improve the robustness of existing and
new equipment to guarantee their usefulness in a future with increased operational
instability. As a part of this improvement process, this work is focused
on the guide/journal bearings which support the rotating portion of power generating
machines. These bearings are studied using using a multi scaled approach
covering small and large scale laboratory experiments as well as investigations
of a full scale machine.
A journal bearing test machine was constructed to investigate a number
of new synthetic lubricants and polymer bearing materials. These tests found
that a significant reduction in power loss could be accomplished without significantly
affecting the bearing’s minimum film thickness by changing from a
traditional mineral oil to a high viscosity index oil of much lower base viscosity
grade. The high viscosity index lubricants were then improved to reduce
start-up friction as well. Further studies were conducted in small scale to determine
the optimum lubricant characteristics for the startup problem. This
knowledge was used to develop new lubricants to test in the journal bearing
test machine which showed large reductions in power loss in the bearing and
pumping system as well as greatly reduced bearing operating temperature.
Further experimental work led to the development of practical guidance
for power plant operators contemplating a lubricant change. This technique
focuses on the importance of maintaining equivalent viscosity in the minimum
film thickness region after a lubricant change. Efficiency improvements can
then be calculated by comparing the viscosity in the bulk of the bearing to that
with the original lubricant.
Experimental work with polymer bearing facing materials demonstrated
the dramatic reductions in break away friction that these materials can provide.
A number of polymer composite materials were investigated for their friction
characteristics at the moment of the start of sliding, finding that PTFE based
materials were far superior to traditional white metal. This work with polymer
faced bearings was extended to testing in a tilting pad journal bearing test rig
which allowed for identification of the dynamic characteristics resulting from
changes in bearing pad material and configuration.
Investigations in the full scale with the Porjus U9 unit provided valuable
insight into the dynamics of a full scale machine as well as needed data for the
improvement of multi-physics models of bearings. Insights from the Porjus U9
experiments clarify many of the design challenges for large journal bearings
in hydro power machines such as the thermal transients during startup and the
dynamic effects during load changes.
The results from this work demonstrate that significant performance improvement
of journal bearings is possible through the use of new lubricants,
materials, and adjustments in operational methods.