“Introduction:

In comparing the equipment of hydro plants to that of thermal plants, the equipment of hydro plants are easier to maintain and operate. From the fuel source (reservoir water VS coal, oil etc.) to fuel handling (headgate-penstock VS conveyer-pulverizer-boiler), from the generation system (high speed turbine-generator VS low speed turbine-generator) to the used energy discharge (condenser VS draft tube), the low speed hydro plant has demonstrated its unique simplicity in maintenance and reliability. It is this simplicity that most of the hydro managing personnel have taken for grant for last 100 years. Traditional maintenance concepts such as run-to-failure or scheduled preventive work prevailed even though such practices were often ineffective at identifying and correcting equipment reliability problems. Reluctance to change and a general lack of knowledge to exploit the benefits of a predictive maintenance program has left many hydro turbine-generator running inefficiently, and sometimes, dangerously.

Facing the challenges of maximizing the remaining useful life of aging equipment and upgrading the turbine-generator capacity using computer modeling, PacifiCorp Hydro Resources department took a giant step in 1992 to replace the outdated scheduled maintenance program with a cost-effective predictive maintenance program which focuses on the broad concepts of cost-reduction, improving equipment reliability, and enhancing safety. As part of the predictive maintenance program, which includes thermal scans, oil analysis, and generator PD testing, the vibration monitoring program has gradually played a significant role in maximizing the remaining useful life of turbine-generators.

System Overview

PacifiCorp Hydro Power consists of 60 medium and small hydro turbine-generators. The total capacity is 1150 MW. There are 28 units rated 15 MW or higher. Most of the slow speed turbines, which are scattered in California, Idaho, Oregon, Utah and Washington states, are vertical reaction-type Francis turbine. A Francis turbine infrastructure consists of a spiral case, a butterfly valve, guide vanes, wicket gates, the turbine runner and a draft tube (Fig. 1 shows a typical Francis turbine system with the generator and lubricating bearings).

Vibration Monitoring Progam

The vibration monitoring program for hydro plants was set up in 1992. With the support of the senior vice president, two HP dynamic spectrum analyzers and structural software were purchased for structural testing and dynamic balancing. A PC-based Entek predictive maintenance software program with a HP portable data collector was used to establish the baseline data and trend the machine conditions. After the baseline data for each piece of equipment was established, the trend data and case histories were used to customize the frequency band alarms and overall alarms of each turbine-generator based on the variety of speed and rotor mass.”