IEEE Std 485-2020 pdf download

IEEE Std 485-2020 pdf download.IEEE Recommended Practice for Sizing Lead-Acid Batteries for Stationary Applications.
c) Frequency and depth of discharge
d) Type of discharge (high-rate, long-duration, mixed loads)
e) Ambient temperature (Note that sustained high ambient temperatures result in reduced battery life. See IEEE Std 484 and IEEE Std 1187.)
f) Charging characteristics
g) Maintenance requirements
h) Cell orientation requirements
I) Ventilation requirements
j) Seismic characteristics
k) Spill management
6. Determining battery size
6.1 General
Several basic tctors govern the size (number of cells and rated capacity) of the battery, including the maximum system voltage, the minimum system voltage, correction factors, and the duty cycle. Because a battery is usually composed of a number of identical cells connected in series, the voltage of the battery is the voltage of a cell multiplied by the number of cells in series. The ampere-hour capacity of a battery is the same as the ampere-hour capacity of a single cell, which depends upon the dimensions and number of plates.
It’ cells of sufficiently large capacity are not available, then two or more strings (equal numbers of series- connected cells) should be connected in parallel to obtain the necessary capacity. The capacity of such a battery is the sum of the capacities of the strings. Consult the manufacturer for any limitation on paralleling.
Examples of conditions that can change the available capacity of the battery are as follows:
The available capacity of the battery decreases as its temperature decreases.
The available capacity decreases as the discharge rate increases.
The minimum specified cell voltage at any time during the battery discharge cycle limits the available
capacity of the battery.
6.2 Numberof cells
6.2.1 General
The maximum and minimum allowable system voltage determines the number of cells in the battery. It has been common practice to use 12, 24, 60, 120, or 240 cells for nominal system voltages of 24 v, 4 V, 125 V. 250 V, or 480 V. respectively. In some cases, it is desirable to vary from this practice to match the battery to system voltage limitations more closely. It should be noted that the use of the widest possible voltage window, within the confines of individual load requirements, results in the most economical battery. Furthermore, the use of the largest number of cells allows the lowest minimum cell voltage and, therefore, the smallest size cell for the duty cycle. The application of the following principles is illustrated in A.2 ofAnnex A.
Furthermore, the use of the largest number of cells allows the lowest minimum cell voltage and therefore, the smallest size cell for the duty cycle.
The cell size calculated for a specific application seldom matches a commercially available cell exactly, and it is normal procedure to select the next higher capacity cell. The additional capacity obtained can be considered part of the design margin.
Note that margins are also discussed in clause 6.3.1.5 and clause 6.3.3 of IEEE Std 323fh [82]. However, those margins are applied during qualification and are not related to the design margins described in this clause.
6.3.4 Aging factor
As a rule, for long-duration discharges of a vented lead-acid battery, the capacity slowly declines throughout most of the battery’s life. hut begins to decrease rapidly in the latter stages. with the “knee” of the life versus capacity curve occurring when the remaining capacity is reduced to approximately 80% of rated capacity. This characteristic is well documented for discharges at the 1 h rate or longer.
flecause of that, IEEE Std 450 and IEEE Std 1188 recommend that a battery be replaced when its actual capacity drops to 80% of its rated capacity. Therefore, to maintain the battery’s capability of meeting its design loads throughout its service life, the battery’s rated capacity should be at least 125% (1.25 aging factor) of the load expected at the end of its service life.
For high-rate, short-duration discharges of vented lead-acid batteries and all discharges of VRLA batteries, there are too many variables to state definitively where the “knee” occurs. Therefore, it is reasonable to expect its short-duration performance to drop significantly below 80% of its rating before it reaches the “knee” at that rate so a larger aging factor may be appropriate. Consult with the battery manufacturer for additional information and recommendations.