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Gregory Simmons (LTU)

Published: 14 October 2013

Journal Bearing Design, Lubrication and Operation for Enhanced Performance

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 instability. While many components in hydropower systems require thorough investigation to improve their robustness, this work is focused on the guide/journal bearings which support the rotating portion of power generating machines.

This work addresses the journal bearing problem through 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 great 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 Babbitt 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.

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.

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.