User's Manual

Operation: Base Metrology
CENTRON® OpenWay™ Meter Technical Reference Guide 19
Block Interval Demand Calculation
Block Demand calculations are based on user-defined interval lengths. The demand is the
total energy accumulated during the interval divided by the length of the interval. At each
end of interval (EOI), demand calculations are made and “EOI” can be displayed on the
LCD.
For block interval, demand calculations are made at the end of each completed demand
interval. This method is similar to the way mechanical demand meters operate. As load is
applied to the demand register, an indicating pointer and maximum demand indicator are
driven upscale. At the end of each interval, the indicating demand pointer is returned to the
zero position, and the maximum demand pointer retains its highest or maximum position.
Rolling/Sliding Demand Interval Calculation
A selected number of subintervals make up the demand interval. At the end of each
subinterval, new demand calculations occur based on the last full demand interval and
“EOI” can be displayed on the LCD.
See Demand Registers (on page 38) for a list of the quantities that can be selected for rolling
demand.
Block interval demand calculation is subject to peak splitting, whereby it is possible for an
electricity consumer to manipulate the load for limited periods within the demand interval.
The registered demand reading will be less than the actual maximum demand of the load.
To counter this situation, the concept of rolling demand was introduced. Rolling demand is
calculated as follows:
1 For illustration purposes, assume a 15 minute billing demand interval with three five-
minute subintervals has been selected. Then, at any given moment, the meter has three
complete sets of five-minute information available for demand calculations.
2 At the end of the present five-minute subinterval, the information on the oldest five-
minute subinterval is discarded, and demand calculations are performed on the three
newest sets of subintervals. In this manner, the CENTRON OpenWay meter with the
rolling demand option updates the demand calculations every five minutes.
3 If the billing demand interval is 30 minutes with five-minute subintervals, then six sets
of five-minute information or updates will be used for calculating previous demand.
Cumulative Demand Values
Cumulative Demand is the summation of previous maximum demands after each demand
reset. When a demand reset occurs, the maximum demand values are added to the existing
corresponding cumulative demand values, and the sums are saved as the new cumulative
demands. These values will not increase until the next demand reset. This feature not only
protects the user from false or erroneous readings, but also provides the customer with extra
security against tampering. Cumulative demand may be used for block, rolling and thermal
demand types.
Draft