IEE 1115a-2007 pdf download IEEE Recommended Practice for Sizing Nickel-Cadmium Batteries for Stationary Applications Amendment 1: Additional Discussion on Sizing Margins
Insert the following subclause heading (with existing text from 6.2.2, changed where noted):
6.2.2.1 General
t is prudent design practice to provide a capacity margin to allow for unforeseen additions to the dcsystem, and less-than-optimum operating conditions of the battery due to improper maintenance, recentdischarge, ambient temperatures lower than anticipated, or a combination of these factors. A method ofproviding this design margin is to add a percentage factor to the cell size determined by calculations. If thevarious loads are expected to grow at different rates, it may be more accurate to apply the expected growthrate to each load for a given time and to develop a duty cycle from the results.
Note that the “margins reuired described by 6.3.1.5 and 6.3.3 of IEEE Std 323-1983 are to be appliedduring “*qualificationand are not related to “design margin.”
The cell size calculated for a specific application will seldom match a commercially available cell exactlyand it is normal procedure to select the next higher cell size. The additional capacity obtained can beconsidered part of the design margin.
Insert the following subclause:
6.2.2.2 Effects of cycling
f a nickel-cadmium battery is used in a stationary application with constant-oltage charging, in whichcharge-discharge cycling occurs, the battery state of charge (SOC) may be affected over time, and theavailable capacity may be reduced. Although the battery can usually be brought back to a full state ofcharge, it may require an off-line high-rate charge. Adjustment of the design margin provides a convenientmethod for compensating for this reduction in available capacity.
The extent to which available battery capacity may be affected depends on the frequency and depth ofcycling, charging regime, and the specific cell design. The battery manufacturer should be consulted for anestimation of the SOC after a specified number of cycles to a specified depth of discharge and based on theexpected temperature,charging voltage(s).and charging time.
The estimated SOC should be expressed as a decimal, typically below 1.00 (an SOC of 1.00 does notrequire any modification of the design margin). Divide the design margin (as discussed in 6.2.2.1, butexcluding the effects of recent discharge) by the SOC to obtain the adjusted design margin:
design margin from 6.2.2.1Adjusted design margin-soc
For example, 10% load growth is expected, so the design margin is 1.10. Because of frequent cycling, themanufacturer expects the battery to operate at 90% SOC. The adjusted design margin is
1.10Adjusted design margin ==1.220.90
IEE 1115a-2007 pdf download
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