Oil conditioner reduces bearing wear, downtime
In the late 1980s, a variety of problems with turbine generator bearings at several sites prompted Florida Power and Light Co. (FPL) to establish a task force, studying the causes and making recommendations. A survey of the company`s 13 fossil and nuclear plants showed a higher rate of bearing wear and shorter bearing life than rates reported by four other major utilities across the country which were contacted by the team. Generators at FPL have capacities ranging from 60 to 800 MW.
A study and analysis of past problems, plus detailed investigations of incidents that occurred after the team was formed, indicated contaminated lubricating oil was the primary cause of accelerated bearing wear, although oil temperature was also a factor.
After several years of study and investigations, the team recommended higher standards for turbine oil contaminants, more frequent sampling and filters to remove smaller particulates.
Change for the better
“We changed from the Society of Automotive Engineers (SAE) class 6 standard to International Standards Organization class 16/13, which is comparable to SAE class 4,” said Douglas J. Whitney, FPL principal engineer and task force member.
The task force investigated five turbine oil conditioning systems. Two were in-line, full filtration systems, working at both the pum¥and bearings. Three were bypass systems.
All five were evaluated for particulate and water removal, capacity, maintenance and operating costs, and safety. The team recommended high capacity, multiphase units with pressure coalescence filters to remove water and 3-micron filters for particulates.
They settled on Kaydon`s Turbo-Toc system, and installed the first one approximately five years ago. The system includes an initial cleanable mesh screen, particulate filters, pressure coalescence filter cartridges and separator elements to remove water, plus a final polishing phase of particulate filters.
Today, FPL has Kaydon systems on all its main turbine/generators and is considering installation on smaller generator units. The utility`s fossil plants have from two to four systems and the two nuclear plants have two turbine/generators each.
The relation of oil contamination to the wear and failure of bearings has been demonstrated by research studies and plant experience for many years. Clean turbine oil is increasingly important because changing power demands require more turbine/generator cycling today than was typical in the past, and cycling puts more stringent requirements on the turbine oil lubrication system and on the filtration system.
Fast removal of contaminants can speed startups after outages. FPL technicians note that repair operations can increase particulate contamination or increase the chance of water leaks. The FPL task force studied particulate contamination from oil-line flushing during major overhaul of one unit. When the oil conditioning system is run continuously during repairs, whether the turbine is operating or not, the oil is kept cleaner for a faster restart.
Problems from water contamination tend to be more damaging than particulate contamination because free and emulsified water can oxidize ferrous components on contact, resulting in more particulates. Also, water is a breeding ground for bacteria, which can cause slime, prematurely blocking particulate filters. The Kaydon systems reduce free and emulsified water to 25 ppm or less for influent water levels u¥to 5,000 ppm. Control panel gauges and lights show the status of the Turbo-Toc units, permitting quick status checks.
“Operation has improved, many nuisance problems have been eliminated, and less work is needed on bearings,” Whitney said. “It is impossible to put exact figures on the savings because costs of problems and repairs can vary so widely, depending on when they occur.” z