8-22
Breaker Monitor and Metering Functions
Date Code 20010625
SEL-311L Instruction Manual
L
OCAL
D
EMAND
M
ETERING
The SEL-311L Relay offers the choice between two types of demand metering, settable with the
enable setting:
EDEM = THM (Thermal Demand Meter)
or
EDEM = ROL (Rolling Demand Meter)
The demand metering settings (in Table 8.3) are available via the
SET
command (see Settings
Sheet at the end of
Section 9
. Also refer to
MET Command [Metering Data]
, MET D—
Demand Metering in
Section 10: Line Current Differential Communications and Serial Port
Communications and Commands
).
The SEL-311L Relay provides local demand and local 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 8.13 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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