Schlumberger Sema SMFMM-1 Manuel D’Utilisation
Theory of Operation
SENTINEL Meter Technical Reference Guide
4-11
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.
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.
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.
subinterval, new demand calculations occur based on the last full demand interval
and “EOI” can be displayed on the LCD.
The following quantities can be selected for rolling demand: W d, W r, W net, Var
Q1-Q4, VA d (arithmetic or vectorial), and VA lagging.
Q1-Q4, VA d (arithmetic or vectorial), and VA lagging.
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.
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:
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.
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 SENTINEL meter
with the rolling demand option updates the demand calculations every five
minutes.
five minute subinterval is discarded, and demand calculations are performed
on the three newest sets of subintervals. In this manner, the SENTINEL 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.
six sets of five-minute information or updates will be used for calculating
previous demand.
Thermal Emulation
The SENTINEL meter will emulate the response of a thermal demand meter for kW
and kVA. This type of demand calculation is approximated exponentially. The
meter will record 90% of a change in load in 15 minutes, 99% in 30 minutes, and
99.9% in 45 minutes. The four characteristics of a thermal demand meter that the
SENTINEL meter will emulate are:
and kVA. This type of demand calculation is approximated exponentially. The
meter will record 90% of a change in load in 15 minutes, 99% in 30 minutes, and
99.9% in 45 minutes. The four characteristics of a thermal demand meter that the
SENTINEL meter will emulate are:
•
Arithmetic phase summation
•
Continuous rolling average demand
•
Response calibrated to RMS values
•
No End-of-Interval (EOI)
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