IEEE 485-2020 pdf free download – IEEE Recommended Practice for Sizing Lead-Acid Batteries for Stationary Applications.
4.2.3 Momentary loads Momentary loads can occur one or more times during the duty cycle but are of short duration, not exceeding 1 min at any occurrence. Although momentary loads may exist for only a fraction of a second, it is common practice to treat each load as if it lasts for a full minute because the battery voltage drop after several seconds often determines the battery’s 1-min rating. When several momentary loads occur within the same 1-min period and a discrete sequence cannot be established, the load for the 1-min period should be assumed to be the sum of all momentary loads occurring within that minute. If a discrete sequence can be established, the load for the period is the maximum load at any instant. Sizing for a load lasting only a fraction of a second, based on the battery’s 1-min performance rating, results in a conservatively sized battery. Consult the battery manufacturer for ratings of discharge durations less than 1 min. Typical momentary loads may inclu
a) Switchgear operations
b) Motor-driven valve operations (stroke time < 1 min)
c) Motorized switch operations
d) Field fashing of generators
e) Motor starting currents
f) Inrush currents
4.2.4 Other considerations The loads applied to the battery are normally categorized as constant power, constant resistance, or constant current. However, for sizing purposes, the loads are treated as constant power or constant current. The designer should review each system to be sure all possible loads and their variations are included. If the loads are solely constant power loads, sizing as described in Annex D is appropriate and simplifies the sizing process.
4.2.5 Duty cycle diagram A duty cycle diagram showing the total load at any time during the cycle is an aid in the analysis of the duty cycle. To prepare such a diagram, all loads (expressed in either current or power) expected during the cycle are tabulated along with their anticipated inception and shutdown times. The total time span of the duty cycle is determined by the requirements of the installation.
4.2.6 Defned loads Loads whose inception and shutdown times are known are plotted on the diagram as they would occur. If the inception time is known, but the shutdown time is indefinite, it should be assumed that the load continues through the remainder of the duty cycle. Similarly, if the shutdown time is known, but the inception is not, it should be assumed that the load begins when the duty profile begins.
4.2.7 Random loads Loads that occur at random should be shown at the most critical time of the duty cycle in order to simulate the worst-case load on the battery. These are noncontinuous or momentary loads as described in 4.2.2 and 4.2.3. To determine the most critical time, it is necessary to size the battery without the random load(s) and to identify the section of the duty cycle that controls battery size. Then the random load(s) should be superimposed on the end of that controlling section as shown in Figure 1 (see 6.4.4).IEEE 485 pdf download.