Two Case Studies for the use of PTFE Thrust Bearings in Hydropower Applications

Introduction

In any hydropower scheme the main load carrying bearings at the interface between stationary and moving parts of the system are of crucial importance to the long-term availability of generating capacity and robustness of supply. The tilting pad, fluid film bearings typically used in hydropower applications are based on wellproven engineering and, in most cases, extremely reliable. Nevertheless, bearing-related problems that thrnaten operations can arise for a variety of reasons. Typical causes are changes in the operating regime of the plant compared with the original specification or engineering interventions, for example in the fotm of design changes, in other parts of the assembly that impact adversely on the overall system.

This paper provides case study descriptions of two such major problems occurring in the main bearings of hydropower equipment. In both cases the problems were resolved by the installation of replacement bearings in which one of the working surfaces is covered with a layer of PTFE (Polytetrafluoroetlrylene). PTFE-faced fluid film bearings have been used for many years in the former Soviet Union, China and Eastern Europe. Advantages claimed for these bearings, in comparison with their conventional, whitemetal (babbitt)-faced counterparts, are increased load carrying capacity in normal use and removal of the need for high pressure oil injection. In conventional whitemetal bearings high pressure oil injection is used to reduce friction at start up, when stopping the bearing and in the course of maintenance procedures that require the main shaft to be rotated.