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8-20
Breaker Monitor and Metering Functions
Date Code 20011205
SEL-311B Instruction Manual
The SEL-311B Relay provides demand and peak demand metering for the following values:
Currents I
A,B,C
I
G
3I
2
Input currents (A primary)
Residual ground current (A primary; I
G
=3I
0
= I
A
+ I
B
+ I
C
)
Negative-sequence current (A primary)
Power MW
A,B,C,3P
MVAR
A,B,C,3P
Single- and three-phase megawatts
Single- and three-phase megavars
Depending on enable setting EDEM, these demand and peak demand values are thermal demand
or rolling demand values. The differences between thermal and rolling demand metering are
explained in the following discussion.
Comparison of Thermal and Rolling Demand Meters
The example in Figure 8.11 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”).
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