Schweitzer Engineering Laboratories SEL-787 - Figure 4.42 Response of Thermal and Rolling Demand Meters to a Step Input

4.65
Date Code 20081022 Instruction Manual SEL-787 Relay
Protection and Logic Functions
Demand Metering
Comparison of
Thermal and Rolling
Demand Meters
The example in Figure 4.42 shows the response of thermal and rolling demand
meters to a step current input. The current input is at a magnitude of zero and
then suddenly goes to an instantaneous level of 1.0 per unit (a “step”).
Figure 4.42 Response of Thermal and Rolling Demand Meters to a
Step Input (Setting DMTC = 15 minutes)
Thermal Demand Meter Response
The response of the thermal demand meter in Figure 4.42 (middle) to the step
current input (top) is analogous to the series RC circuit in Figure 4.43.
Thermal Demand
Meter Response
(EDEM = THM)
Thermal Demand Current (per unit)
0
051015
0.5
0.9
1.0
Time
(Minutes)
Rolling Demand
Meter Response
(EDEM = ROL)
Rolling Demand Current (per unit)
DMTC = 15 minutes
0
051015
.33
.67
1.0
Time
(Minutes)
Step Current
Input
Instantaneous Current (per unit)
0
051015
0.5
1.0
Time
(Minutes)