Adjusting Steady-State and Transient Thrust as Part of a Pump Turbine Upgrade

摘要

Hydraulic thrust can vary dramatically as a pump turbine is run over the entire range of pump and turbine operation. The proper design and control of both the upthrust and downthrust is critical to ensuring that the thrust bearing and the powerhouse structure can safely handle the loads. As part of the Rocky Mountain upgrade the pump turbine hydraulic thrust was evaluated and significantly modified to ensure safe long term operation of these 400MW units. Hydraulic thrust is significantly influenced by runner seal location, the design of the crown thrust relief holes, and the design of the equalizer lines. For the Rocky Mountain upgrade all three were redesigned to properly control both the steady-state and transient thrust. In this paper the design, the model test results, and the field test results will be compared to demonstrate how well the thrust can be controlled. The difficulty in the accurate calculation and measurement of thrust both in the field and in the model test results from the delicate balance of very large forces above the crown and below the band. To be confident that the final thrust was optimized, adjustments in the field were planned as part of the upgrade. Field measurements of thrust before and after the upgrade demonstrate the effectiveness of the redesign. These measurements were based on “spring constant,” calculated from a Finite Element model of the thrust bridge, and confirmed with field dead-weight testing. The thrust redesign allowed for elimination of the equalizer line for pump operation. This had the very positive effect of stabilizing flow below the runner (at the entry point of the equalizer line) which significantly reduced localized cavitation near the runner band.