4.155
Date Code 20170927 Instruction Manual SEL-751 Relay
Protection and Logic Functions
Group Settings (SET Command)
Comparison of Thermal and Rolling Demand Meters
The example in Figure 4.91 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 4.91 Response of Thermal and Rolling Demand Meters to a Step Input
(Setting DMTC = 15 minutes)
Thermal Demand
Meter Response
(EDEM = THM)
Thermal Demand Current (per unit)
0
0 5 10 15
0.5
0.9
1.0
Time
(Minutes)
Rolling Demand
Meter Response
(EDEM = ROL)
Rolling Demand Current (per unit)
DMTC = 15 minutes
0
0 5 10 15
.33
.67
1.0
Time
(Minutes)
Step Current
Input
Instantaneous Current (per unit)
0
0 5 10 15
0.5
1.0
Time
(Minutes)