O&M – Balance of Plant: Walter M Higgins Generating Station
ACC gear-reducer condition-based maintenance
Water M Higgins Generating Station
NV Energy
530-MW, gas-fired, 2 × 1 combined cycle located in Primm, Nev
Plant regional director: Tom Price
Key project participants: Dave Rettke, maintenance specialist; Entire Higgins staff
Challenge. The ACC’s 510 × 178-ft main operating deck stands over 60 ft in the air and supports 40 35-ft-diam and two-speed motor that run as needed when the plant is in operation.
The ambient environment is harsh. Temperatures range from 115F in summer to about 20F in winter. The drive unit, including the gear reducer, sits in the middle of the air stream. Each gear reducer requires about 7.5 gallons of Mobilgear Synthetic SHC XMP 320, which has a viscosity similar to that of honey.and two-speed motor that run as needed when the plant is in operation.The ambient environment is harsh. Temperatures range from 115F in summer to about 20F in winter. The drive unit, including the gear reducer, sits in the middle of the air stream. Each gear reducer requires about 7.5 gallons of Mobilgear Synthetic SHC XMP 320, which has a viscosity similar to that of honey.
Solution.
The Higgins O&M staff took ownership of the entire plant during construction and through commissioning. It was decided that a condition-based maintenance program would be integral to maintenance activities and operation of the plant as a whole.
Since the lubricant chosen and accepted by the manufacturer of the gear reducers is more expensive than the usual oil, a joint decision to service each gear reducer according to condition was decided as a best practice to significantly lower operational cost. To achieve this, a sampling/filtering program was developed that would allow maintenance staff the ability to determine the condition of the gear reducer and the lubricant in the best scientific way possible.
Twice a year each gear reducer has an oil sample taken, and immediately after sampling, a portable filter cart is connected directly to the gear reducer. The filter cart’s dual filters have the ability to filter down to 10 microns and also remove up to one gallon of water per filter.The samples are sent in for analysis and the results are checked for optimal operation. If a sample shows high water or contaminant levels, a second sample is drawn. Since filtering occurs right after sampling, the second sampling will show the results of that filtering and if further work is necessary.
The reasoning behind the sampling and filtering program put in place includes the following:
- First is the location of the gear reducers. The ACC structure makes “usual” maintenance difficult at best, making the fewest possible gear-reducer replacements desirable.
- Second, the manufacturer’s recommendations are to change the oil every 5000 hours or 18 months of operation at a cost of $21,760 in material with oil at $68/gal. With 40 gear reducers, each requiring eight gallons of oil, the plant needs to purchase 320 gallons of oil.
- Third, changing lube oil on an hourly based schedule isn’t have shown historically that oil is often changed long before needed. By sampling, the plant can see the actual condition of the oil and know whether or not it needs to be changed.
Results.
Since commissioning, only three gear reducers and one oil pump have been replaced. New oil for these fans, plus replacement oil for six other gear reducers in accordance with sampling results, add to a total oil cost of around $5440.
The plant has been in operation since 2004 and there has been only one complete change of lubricant for all 40 gear reducers—the initial 400-hr change. Since then, sampling and filtering have kept changes down to 10 gear reducers, or about 80 gallons of oil.
Had time-scheduled oil changes been implemented, the cost of the estimated four complete changes of lubricant (after the initial 400-hour change) would have been $87,040. The total saving on lubricant alone has been $81,600. This does not include man hours or other ancillary expenses that occur with scheduled maintenance.
