4.154
SEL-751 Relay Instruction Manual Date Code 20170927
Protection and Logic Functions
Group Settings (SET Command)
The demand current level settings are applied to demand current meter outputs
as shown in Figure 4.90.
Figure 4.90 Demand Current Logic Outputs
For example, when residual ground demand current IGD exceeds correspond-
ing demand pickup GNDEMP, Relay Word bit GNDEM asserts to logical 1.
Use these demand current logic outputs (PHDEM, GNDEM, and 3I2DEM) to
alarm for high loading or unbalance conditions.
The demand values are updated approximately once a second. The relay stores
peak demand values to nonvolatile storage every six hours (it overwrites the
previous stored value if it is exceeded). Should the relay lose control power, it
restores the peak demand values saved by the relay.
Demand metering peak recording is momentarily suspended when SEL
OGIC
control equation setting FAULT is asserted (= logical 1). The differences between
thermal and rolling demand metering are explained in the following discussion.
Table 4.57 Demand Meter Settings
Setting Prompt Setting Range
Setting Name :=
Fac to ry Defa ult
ENABLE DEM MTR THM, ROL EDEM := THM
DEM TIME CONSTNT 5, 10, 15, 30, 60 min DMTC := 5
PH CURR DEM LVL OFF, 0.50-16.00 A
a
OFF. 0.10-3.20 A
b
a
For I
NOM
=5 A.
b
For I
NOM
=1 A.
PHDEMP := 5.00
a
PHDEMP := 1.00 b
RES CURR DEM LVL OFF, 0.50-16.00 A
a
OFF, 0.10-3.2 A
b
GNDEMP := 1.00
a
GNDEMP := 0.20
b
3I2 CURR DEM LVL OFF, 0.50-16.00 A
a
OFF, 0.10-3.2 A
b
3I2DEMP := 1.00
a
3I2DEMP := 0.20
b
PHDEM
Relay
Word
Bits
Demand Current
Pickup Settings
(A Secondary)
IBD
IAD
IA
ICD
Analog
Quantities
Demand
Currents
Instantaneous
Currents
Serial Port
Command
Demand Function
Maximum
Current
Logic
Thermal (EDEM = THM)
or
Rolling (EDEM = ROL)
Reset
Demand
PHDEMP
IGD
Reset
Demand
Thermal (EDEM = THM)
or
Rolling (EDEM = ROL)
GNDEM
GNDEMP
IG
(residual)
Demand Function
3I2D
Reset
Demand
Thermal (EDEM = THM)
or
Rolling (EDEM = ROL)
3I2DEM
3I2DEMP
3I2
MET RD
Demand Function
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