Electro Industries/GaugeTech Nexus 1250, Installation & Operation Manual

Page: 22 / 115

e
Electro Industries/GaugeTech
Doc #: E107-7-06-121
2-6
2.3: Demand Integrators 2.3: Demand Integrators
Power utilities take into account both energy consumption and peak demand when billing customers.
Peak demand, expressed in kilowatts (kW), is the highest level of demand recorded during a set period
of time, called the interval. The Nexus 1250 supports the following most popular conventions for
averaging demand and peak demand: Thermal Demand, Fixed Window Demand, Sliding Window
Demand and Predictive Window Demand. You may program and access all conventions concurrently
with the Nexus Communicator software (see the
Nexus Communicator User Manual ).
n
Thermal Demand : Traditional analog watt-hour (WH) meters use heat-sensitive elements to
measure temperature rises produced by an increase in current flowing through the meter. A pointer
moves in proportion to the temperature change, providing a record of demand. The pointer remains
at peak level until a subsequent increase in demand moves it again, or until it is manually reset. The
Nexus 1250 mimics traditional meters to provide Thermal Demand readings.
n
Fixed Window Demand : This convention records the average demand for consecutive time
intervals (usually 15 minutes). For example, if the user selects fifteen-minute intervals and begins
measuring at 12:00, the first window will be from 12:00 to 12:15, the next window will be from
12:15 to 12:30 and, so on.
n
Rolling Window Demand (Sliding Window) : The Rolling Window convention divides a fixed time
interval into a programmable number of subintervals. The Nexus calculates the average demand at
the end of each subinterval. At the conclusion of the time interval, all calculations from the
subintervals are totaled and averaged together. This provides a more accurate demand reading than
Fixed Window Demand.
n
Predictive Window Demand : Predictive Window Demand enables the user to forecast average
demand for future time intervals. The Nexus uses the delta rate of change of a Rolling Window
Demand interval to predict average demand for an approaching time period. The user can set a relay
or alarm to signal when the Predictive Window reaches a specific level, thereby avoiding
unacceptable demand levels. The Nexus 1250 calculates Predictive Window Demand using the
following formula:
(Thermal Avg. x Time Left in Sub-Interval) + (Accumulated Value in Period) + [Prev. SWD x (# of Sub-Intervals-1) x Sub-Interval Length]
Total Sliding Window Demand Period
Courtesy of NationalSwitchgear.com