Demand functions, Demand reporting, Demand calculation and reporting – Basler Electric BE1-851 User Manual
Page 109: Demand functions -7, Demand reporting -7, E1 k
this section. As with other commands, a combination read command is available to read several items in
a group. If the command RG is entered by itself, the relay reports the time, date, target information, and
other reports in the following example. RG-VER and RG-STAT commands have multiple line outputs and
these are not read at the RG command.
Demand Functions
Demand Reporting
The demand reporting function continuously calculates demand values for the three-phase currents,
neutral current, and negative-sequence current. Demand values are recorded with time stamps for Peak
Since Reset, Yesterday’s Peak, and Today’s Peak. Programmable alarm points can be set to alarm if
thresholds are exceeded for overload and unbalanced loading conditions.
Demand Calculation and Reporting
An algorithm in the demand reporting function digitally simulates a thermal or exponential response. An
exponential algorithm computes demand values with the demand interval or response period defined as
the time taken by the meter to reach 90 percent of the final value for a step change in the current being
measured. Demand interval can be set independently for the phase, neutral, and negative-sequence
demand calculations. The reactive power and power demand intervals always match the phase demand
interval setting.
The following equation is used to calculate demand current:
(
)
1
n
n
n
DI
MI
K
1
DI
DI
−
−
+
−
=
Equation 6-1. Demand Current Equation
Where:
n
DI
=
Demand current for sampling period n
(
n
t
=
15 seconds
)
n
MI
=
Average metered current value for sampling period n
K
=
Exponential response constant
The following equation is used for
K
:
−
=
−
I
n
T
434
.
0
t
e
1
K
Equation 6-2. Exponential Response Constant
Where:
I
T
= Demand interval (programmed with SG-DI command)
n
t
= Fixed demand update rate of 15 seconds
Demand is calculated for a step change in current by the following equation:
MI
e
1
DI
I
n
T
434
.
0
t
−
=
−
Equation 6-3. Step Change Demand Calculation
Demand calculation example for a step change in current:
9289900990 Rev R
BE1-851 Reporting and Alarms
6-7