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8.20
SEL-311C Relay
Instruction Manual
Date Code 20060320
Breaker Monitor and Metering Functions
Demand Metering
Demand Metering
The SEL-311C 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
) are available via the
SET
command (see
Other Enable Settings on page SET.2
and
Settings (See Figure 8.11 and Figure 8.13) on page SET.14
. Also refer to
Command (Metering Data) on page 10.20
and
).
The SEL-311C provides demand and peak demand metering for the following
values:
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
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”).
Currents
I
A,B,C
Input currents (A primary)
I
G
Residual ground current (A primary; I
G
= 3I
0
= I
A
+ I
B
+ I
C
)
3I
2
Negative-sequence current (A primary)
Power
MW
A,B,C,3P
Single- and three-phase megawatts
MVAR
A,B,C,3P
Single- and three-phase megavars
Summary of Contents for SEL-311C
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