In the previous two installments of "Competitive Maintenance Strategies," we examined several best practices that should be part of the workday routine for high-performing plants. In Part I, we discussed the characteristics of a good reliability-centered maintenance program, the use of root-cause analysis as a maintenance tool, and ways to improve your predictive maintenance program (March 2010). In Part II, we focused on combined-cycle plants, especially heat-recovery steam generators, to identify several operating practices that are directly linked to the cost of plant maintenance. One specific area discussed was the need for a good valve maintenance program (April 2010). This third and final installment addresses three more areas where an investment in good maintenance practices pays operating availability dividends.
Give Batteries More than Specific-Gravity Tests
The time-honored method of assessing the overall condition of lead acid, wet-cell battery banks is to manually measure cell voltage, current, and electrolyte specific gravity, and to visually check fluid level and terminal post connections. While this is satisfying to some, most experts say that you should conduct more tests to get a true measure of the health of their batteries.
One way to do this is to deep-discharge new batteries once every five years, increasing the frequency of deep-discharge later, as the batteries reach the end of their 20-year life. A typical flooded-cell battery is rated for 50 deep discharges in its 20-year life, so 10 to 15 deep discharges for testing are not detrimental to the battery. In addition, a discharge serves to agitate the electrolyte, which is good for the battery.
But many substation engineers are opposed to deep discharges, partly because they feel this takes away from the life of the battery, and also because the battery string must be taken off-line to discharge it. Discharge tests are costly as well, because a utility must invest in its own battery-loading bank to absorb the energy. Consequently, utilities have always wanted a simpler indicator of battery strength and remaining life that is easy to apply, less labor-intensive, and less risky to both personnel and batteries.
Hence, battery monitors, as contrasted with single-function testing devices, should be included in any battery room. Single-function testers, such as hydrometers or voltmeters, check just one parameter, such as specific gravity or voltage. By contrast, battery monitors continuously check a variety of parameters, such as voltage, temperature, fluid level, float current, and cell impedance or resistance. Two developments have promoted the use of monitors: automation through electronic sensors coupled with computers, and the downsizing of large, labor-intensive maintenance organizations to reduce costs.
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