When upgrading generator excitation systems to electronic static exciters, power plant operators must address the mechanical equipment left behind.
In the case of a generator with collector rings, one option is to leave the old mechanical rotating elements in place. If left in place, they provide no benefit yet can be expensive nuisances to maintain. On the other hand, a brushless generator does not possess collector rings so the operator must add a new collector shaft. In both cases, the overhung slip ring shaft must be considered.
While in theory an overhung collector shaft could be left unsupported, this can unexpectedly become an operational and maintenance nightmare with all but very short overhung shaft lengths of any diameter. Another possibility is to relocate an existing exciter bearing to support the overhung collector shaft, but this has met with limited success. Old exciter bearings have difficulty with the misalignment and loading conditions that are present with rotor configurations for which they were not designed.
Though the preferred objective is a single bearing carrying the overhung collector shaft, ordinary mechanically-pivoted tilt pad exciter bearings offer only a partial solution to the problems at hand. It is true that, by design, a tilting pad radial bearing will handle the stability requirements that are present in a steady rest application. Yet, unfortunately, it may be unable to accommodate the alignment variations or provide adequate stiffness for the load variations that are typically associated with this application. Moreover, fretting of the mechanical pivots changes bearing clearances over time. Problems arise over the long term application of conventional tilting pad bearings as exciter steady rest bearings and explain why they are a source of common concern among end users.
Pioneer Motor Bearing’s proprietary Fluid Pivot® JS Tilt Pad Bearing is an ideal design to support overhung shafts and accommodate severe misalignment. Our original Fluid Pivot JC Tilt Pad Bearing has proven itself over 30 years in rotating equipment. Now, our advanced Fluid Pivot JS design offers a vastly enhanced ability to accommodate misalignment.
Our Fluid Pivot JS bearing features spherically-seated pads continuously floating on hydrostatic oil films that are self-generated (not by external pressure requiring a separate pump, oil lines, etc.). The result? Fluid Pivot JS can extend misalignment capability to an astonishing 1 inch in 12 inches, or 5.0°. That means that our Fluid Pivot JS bearing provides unprecedented dynamic alignment, not alignment merely for the limited purpose of installation. Supported by a hydrostatic film of oil, the pads have more tolerance for operational misalignment, thermal distortion and load stresses than conventional, essentially dry (“arthritic”), spherical seated bearings, including ball and socket bearings and ordinary tilting pad bearings.
A Turnkey Package of Engineering Services
To provide the customer with a complete turnkey package and undivided responsibility, we start by performing a careful rotordynamics and shaft elevation investigation for each application. We’ll consider the foundation and, as necessary, perform a finite element analysis in order to design an appropriate supporting fabrication. A supporting pedestal with instrumentation and lubrication connections completes the mechanical package where the collector shaft already exists. A skid-mount, collector- shaft, brush-rigging, and Fluid Pivot® JS bearing provide the mechanical package for a brushless-exciter replacement.
Pioneer’s turnkey solution to replace an end-user’s existing exciter mechanical components with a full mechanical upgrade includes:
- On-site investigation
- Rotordynamics evaluation
- Finite element analysis
- Removal of old exciter mechanical components
- Delivery of hardware:
- Fluid Pivot JS tilting pad journal bearing
- Single or double insulated
- Housing with seals
- Pedestal (with instrumentation and lubrication connections)
- Collector shaft, brush rigging, and skid, as needed
- Shaft Instrumentation
- Installation of pedestal, housing, bearing and shaft (by qualified overhaul specialist sub-contractors)
- Technical oversight at start up