Rockwell Automation Publication 1426-UM001J-EN-P - August 2019 83
Metering Chapter 4
Demand Metering
Demand is an electric power term that expresses the average energy usage over a
predefined period. Your electrical energy provider specifies how demand is
determined in the rate tariff or schedule that is used to calculate your electric bill.
The power monitor can be configured to align with how your electric-energy
provider measures demand by using a fixed demand period or a sliding time
window. The demand period can be configured to be timed internally,
synchronized to an external demand end-of-interval contact connected to the S2
status input, or synchronized by using communication. The PowerMonitor 5000
unit, by default, calculates demand on a fixed 15-minute demand period, which is
synchronized to the power monitor internal clock.
Projected demand calculates an instantaneous or linear projection of demand at
the end of a demand interval.
Demand power factor is calculated by using the following formula.
Demand Calculation
Demand is equal to the average power level during a predefined time interval.
This interval continuously repeats and is typically 15 minutes but can be 5...30
minutes in length. The power monitor computes demand levels for watts, VA,
amps, and VARs, and provides two different methods for projecting demand.
The formula for real power (kW) demand is the following.
T = Demand interval duration
T = Time at beginning of interval
P(t) = Power as a function of time
Table 9 - Demand Metering Metered Parameters
Parameter Description Range Units
kW_Demand The average total real power during the last demand period. ± 0.000…9,999,999 kW
kVAR_Demand The average total reactive power during the last demand period. ±0.000…9,999,999 kVAR
kVA_Demand The average total apparent power during the last demand period. 0.000…9,999,999 kVA
Demand_PF The average PF during the last demand period. -100.0…100.0 PF
Demand_Amperes The average demand for amperes during the last demand period. 0.000…9,999,999 A
Projected_kW_Demand The projected total real power for the current demand period. ± 0.000…9,999,999 kW
Projected_kVAR_Demand The projected total reactive power for the current demand period. ±0.000…9,999,999 kVAR
Projected_kVA_Demand The projected total apparent power for the current demand period. 0.000…9,999,999 kVA
Projected_Ampere_Demand The projected average amperes for the current demand period. 0.000…9,999,999 A
kWDemand
kVADemand
----------------------------------
Demand
1
T
---
Pt()td
t
tT+()

×=
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