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 cycle of operations so that normal permutations and combinations of loads are
encountered. Depending on the facility, a full cycle may be a day, but more
likely a week, and sometimes a complete month or billing period is required.
Figure 9-18 shows a typical situation with three substations and three feeders
per substation. The survey should begin at the utility service entrance.
2.1.1 Service Entrance. A utility service entrance demand profile gives
considerable information about the overall plant. If it peaks radically at a
few places then demand leveling could lead to a reduction in demand charges,
unless the peaks are being caused by individual or allied pieces of equipment
which must operate together. It may be profitable to shift these loads to a
reduced demand charge offpeak period, if the rate schedule includes such
time-dependent provisions. If the demand profile is reasonably level, it may
indicate no need for load shifting.
2.1.2 Substation and Feeders. In Figure 9-18, the demand of the three
substations and the individual feeders supplied by the substations are
monitored. Provided that the demand studies are carried out at comparable
times in the plant operating cycle, and that successive operating cycles show
reasonable consistency, the three substation demand profiles should be roughly
equal to the overall plant profile. The sum of the individual feeder profiles
should roughly equal the respective substation demand profile. Figure 9-19
shows this concept for substation No. 2 and feeders 2A, 2B, and 2C. These
plots were obtained on four successive Wednesdays from data obtained by
monitoring the three feeders and the substation output from 8:00 AM to 8:00 PM.
FIGURE 9-18.
Three Substations With Three Feeders Per Substation
9-43
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