Power Measurement ION 8000 Series - Demand Forgiveness

ION 8000 Series User Guide Demand Forgiveness
Chapter 9 - Demand Page 119
Demand Forgiveness
Demand Forgiveness is the time programmed to the meter during which demand
(and therefore peak demand) will not be calculated in the power restoration period
following a total power outage.
During power-up following a complete power outage, customer equipment
consumes a higher than normal amount of power. The Demand Forgiveness
feature lets a utility forgive the customer for peak demand penalties that may arise
from power-up following a power outage (should the outage exceed a user-
specified period of time).
Demand and Peak Demand Module Overview
Power utilities generally bill commercial customers based on their peak usage
levels, called peak demand (in kW), and energy consumption (in kWh). Demand is a
measure of average power consumption over a fixed time interval, typically 15
minutes. Peak (or maximum) demand is the highest demand level recorded over
the billing period. Sliding window/rolling block demand is one method of measuring
demand.
To compute sliding window demand values, the Sliding Window/Rolling Block
Demand module uses the sliding window averaging (or rolling interval) technique
which divides the demand interval into sub-intervals. The demand is measured
electronically based on the average load level over the most recent set of sub-
intervals.
In the following diagram, the Sliding Window/Rolling Block module labeled
“Demand” calculates demand from the power input by measuring and averaging
the power over a set interval. The demand value is then output to a Maximum
module labeled “Peak Demand” that records the highest demand value over time
(peak demand).
For information on ION modules, refer to the online ION Reference.
Demand and Peak Demand Module Behavior During Demand Forgiveness
A peak demand value is the highest demand value since the last peak demand
reset. The Demand Forgiveness framework sets the Sliding Window/Rolling Block
module (and the Thermal Demand module) inputs to zero during a Demand
Forgiveness period. This method allows demand interval data to accurately reflect
a complete interval that includes data:
 prior to an outage
 during the Demand Forgiveness period (zero values)
 after the Demand Forgiveness period
Maximum
value
(Peak)
(Maximum module)
PEAK DEMAND
DEMAND
(Sliding Window/
Rolling Block module)
Power
Power output
averaged
(Demand)