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
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
(middle) to the step
current input (top) is analogous to the series RC circuit in
Thermal Demand
Meter Response
(EDEM = THM)
Thermal Demand Curr
ent (per unit
)
0
0
5
10
15
0.5
0.9
1.0
Time
(Minutes)
Rolling Demand
Meter Response
(EDEM = ROL)
Rolling Demand Curr
ent (per unit
)
DMTC = 15 minutes
0
0
5
10
15
.33
.67
1.0
Time
(Minutes)
Step Current
Input
Inst
ant
aneous Curr
ent (per unit
)
0
0
5
10
15
0.5
1.0
Time
(Minutes)
Summary of Contents for SEL-787
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