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Steady Rest Bearings (extension shaft bearings)

Many turbines have long extension shafts, often approximately 6 feet long or longer, that are attached to the HP Turbine rotor and extend through the front standard.  In almost all cases, the overspeed bolt and the main oil pump are mounted on this shaft, and in some cases, the thrust bearing runner is included as well. 

For many reasons, at 3600 rpm and generally due to unbalance of the rotors and marginal control of the resulting rotor vibrations, these extension shafts vibrates excessively, causing wear to the seal rings (aka "wear rings") of the main oil pumps.  

A number of turbines have extension shafts that extend through the front standard and drive large high powered fluid drives through flexible couplings.  Westinghouse turbines use steady rest bearings to support the end of the extension shafts for these applications.  The Westinghouse steady rest bearing design uses four small tilting-pads with small diameter rod supports that often pound out within a short time from being installed, whether new or after being renewed.Another extension shaft application that occurs with increasing frequency today has to do with the collector extension shafts outboard of generators.  This occurs because rotating exciters that supported these collector extension shafts are being removed and solid-state excitation systems are being installed.  This leaves these extension shafts unsupported or inadequately supported at the ends so they experience high amplitude vibrations.  Serious consequences are that the collector brushes wear rapidly and the collector rings wear in a non-uniform pattern, often with a 2 per rev wear pattern, due to the two-pole design of the generator rotors with the inherent 2 per rev bending stiffnesses.

TRI's solution is to provide heavy-duty bearings and supporting pedestals of appropriate designs.  TRI has manufactured numerous steady rest bearings and associated pedestals for the extension shafts of Westinghouse turbines.  TRI now has a repertoire of parts from which an assembly of parts is selected.  Certain TRI bearing designs bolt right onto the front walls where the existing 4-pad Westinghouse bearings are attached.  
Where there is no fluid drive, the extension shaft is wholly within the front standard and a new pedestal extending from the floor to the new TRI bearing is required.  These have proven to suppress the rotor vibrations to the point of eliminating wear of the pump seal rings, one of the most common causes of reduced availability of turbine-generators.
If desirable, TRI can manufacture and supply new extension shafts, and if desired, with an integral multi-tooth wheel for electronic speed and overspeed control.
TRI's solutions for solving the vibration issues of collector extension shafts generally include these activities:
  • Assuring that there is a journal surface that is concentric to the extension shaft and collector rings.  This may involve "in-place machining" of the existing rotor, or adding on a short extension shaft with a qualified round and concentric journal surface.
  • A TRI Tilting pad bearing of heavy duty design.
  • A pedestal that extends from the new TRI bearing down to a sole plate.
  • A sole plate, if necessary. 
TRI also provides Technical Direction service for installation of our Bearings and other products.

More Information

Catalogs

Tech Notes

Tech Note March 2005: Solutions For Common Problems of Extension Shafts, Oil Pumps and Steady Rest Bearings For Westinghouse Large Steam Turbine Generators

Tech Note June 2016: Pressure Dam & Elliptical Bore Bearings