Large thrust bearings are highly loaded machine elements and their failures cause seriouslosses. Start ups and stoppages of the bearing under load are specially critical regimesof operation. Load carrying capacity depends on the profile of the oil gap. In transientstates this profile is also changing. In the design of large thrust bearings minimizingthermo-elastic deformations is an important goal, which can be accomplished due toapplication of advanced models of the bearing. Modeling of transient states becomes evenmore complex since there is a dynamic development of temperature distribution anddeformations. Often hydrostatic jacking systems are also used. It seems to the authorsthat advanced bearing models are applied only in research and development of the bearingswhile very simple modeling is applied in on-line analysis of data from monitoring systems.Analysis of the measurement data with the use of more sophisticated models may be helpfulin assessment of current bearing status – especially in early warning. Material issuescreate a separate problem for modeling, being more important nowadays as polymer linedbearings come into use. The models used for polymer lined bearings require realistictreatment of heat exchange and resilience of the bearing surface layer.

A special instrumented pad was installed at hydrodynamic thrust bearing of 125 MW pump turbine in one of Polish power plants. “Spring mattress” type thrust bearings of these machines are quite heavily loaded and have caused many problems so far. It was intended to assess bearing present state more thoroughly than with the use of standard monitoring system and to assist in bearing research and development attempts. Instrumentation of the pad comprises 16 thermocouples for measurements of temperature distribution in the pad and 3 proximity probes to evaluate the pad position and film thickness. The pump-turbine with an instrumented bearing was tested at various operating conditions including steady state and transient conditions. One of the examples of the research carried out with the use of the described instrumentation was the research into the influence of hydrostatic jacking pump operation period on bearing performance in transient states which is presented in the paper. The results showed that current practice of pump operation is far from optimum, and that bearing reliability could be improved by changing the current start-up and coasting procedures. The results also showed that pad position during operation is not satisfactory and also some improvement could probably be achieved by rearranging the support of the bearing pad.