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Q: What weighs more than a locomotive and spins at 3,600 rpm?
A: The rotor in a large steam turbine generator.
Turbines are supported by a series of forcefed plain bearings. The sump used to supply the necessary quantities of lubricant to these bearings can range from a few thousand to as much as 20,000 gallons.
If there is a break anywhere in the oil supply system, then the turbine must trip off or will likely suffer catastrophic damage. In addition to the obvious mechanical damage to the bearings, there is also a serious fire hazard.
Lubrication, hydraulic, control and seal oil fires occur more often than most utilities let on. In many cases, only fires or other incidents that result in downtime are reported or noted. What is the typical cause of oil release that leads to fires in power generating facilities? According to FM Global statistics, oil releases are most often caused by:
This article reflects how FM Global is contributing to identification and reduction of the risk associated with oil related fires in power generation facilities.
Three-dimensional Spill Fire
Inadequate fire-protection systems and a lack of proper emergency protocols can lead to serious damage and extended outages in the event of a lube-oil fire. In a 15-year period, FM Global found that fire protection deficiencies for lube-oil systems were a major factor in 17 large turbine building fires.
The property damage alone (not including business interruption losses) totaled more than 400 million U.S. dollars. Lost generating capacity was in excess of 20 million MWh (assuming a base-loaded station with a capacity factor of 86 percent), which is equivalent to the annual generating capacity of a mid-sized investor-owned utility.
The average property loss from these incidents was more than 26 million dollars. The turbines involved were out of service from 10 days to 48 weeks, with an average downtime of more than 24 weeks. Additionally, three turbines were retired following two large fires.
By contrast, in six turbine-building fires where recommended protection was installed, the average property damage was $700,000 and turbines were out of service from one to seven weeks, with an average downtime of less than two weeks. While this still represents a substantial loss, it is far less than those for under-protected facilities.
These losses do not take into account the additional costs of business interruption and the possible penalties imposed by contractual obligations such as service guarantees, fuelpurchasing arrangements and the many other factors that an increasingly deregulated power industry faces.
Why do these losses continue to occur? One key factor is the lack of definitive research concerning the specific fire threats faced by the power generation industry.
To help refine its knowledge of the fire hazards faced by power producers, FM Global conducted extensive testing at the company’s research campus in West Glocester, Rhode Island.
Impetus for the test program came directly from FM Global power industry clients, many of whom urged the company to conduct this type of research to help them better assess the risks in their facilities. Initially, FM Global intended to demonstrate to clients the significant fire risks.
However, early in the planning process, the effort was expanded to include a research component consisting of full-scale fire tests using the large burn laboratory.
FM Global researchers such as Christopher Wieczorek (senior scientist), Paul Dobson (senior engineer) and Glenn Mahnken (engineering specialist) were responsible for the design of the mock-up generator. They worked with other parties to develop representative scenarios using actual failure cases and field observations to define the three representative fire scenarios as the framework for the research:
three-dimensional spill fires
The researchers also worked with Dennis Waters, research campus manager, on the final design for a mock-up of a small power generation hall. The mock-up design included:
high- and intermediate-pressure turbine housings
grated walkway to simulate an open-floor design
lube oil tank and pumping unit
dike surrounding the lube oil tank
According to Wieczorek and Newman, the fire test program confirmed the following about turbine-hall fire hazards from pressurized-oil systems used in bearing lubrication, seal oil, hydraulics or control systems:
Spray fires and three-dimensional spill fires cannot be extinguished by sprinklers alone.
Oil flow must be cut off as quickly as possible.
Local protection is required to control spray and three-dimensional spill fires.
Pool fires alone can be extinguished by adequate local fire protection.
“We knew the spray fires would be intense. During these fires, we saw ceiling temperatures reach nearly 1,500°F (816°C) without sprinklers turned on and only slightly less with the sprinklers,” Wieczorek said, adding that temperatures above 1,000°F (538°C) can lead to steel deformation and roof failure.
Prior to the research program and subsequent demonstrations, Wieczorek was surprised that many of those he spoke with in the power generation industry underestimated the fire risks posed by lube oil and other systems.
“That was an eye-opener,” he said. “I believe those who see the results of our research and videos of the fire tests, and those who saw our demonstrations in August, have a better understanding of the risks posed by pressurized-oil systems.”
Terry Cooper, FM Global’s industry engineering leader, presented FM Global’s research findings in early September to a gathering of 100 utility representatives from 40 firms at a biannual meeting at the Edison Electric Institute (EEI).
“When we finished describing the research and summarizing our findings, we opened the floor to questions and answers – urging the representatives to try to poke holes in our work,” Cooper said. “There was almost no dissent. They asked many ‘what if’ questions to see how these results applied to their particular situations.”
According to Cooper, “They wanted to know how to evaluate their own risks and protection systems, and learn how to apply this information. This is really a win-win for all concerned. In the case of lube-oil fire hazards, we’ve resolved an issue not only for our clients, but for the entire power generation industry.”
© 2005 Factory Mutual Insurance Company. Reprinted with permission. www.fmglobal.com from Record, volume 81, number 4, 2004.