Schweitzer Engineering Laboratories SEL-421-4 - Page 1033

7.9
Date Code 20171006 Instruction Manual SEL-400 Series Relays
Metering
Demand Metering
NOTE: Changing EDEM or DMTC
resets the demand meter values to
zero. This also applies to changing the
active settings group where either
setting EDEM or DMTC is different in
the new active settings group.
(Changing demand current pickup
settings PDEMP, GDEMP, and QDEMP
will not affect the demand meters.)
Figure 7.5 shows how the relay applies the demand current pickup settings over
time. When residual ground demand current IG(DEM) exceeds the correspond-
ing demand pickup setting GDEMP, Relay Word bit GDEM asserts to logical 1.
Use these demand current logic outputs (PDEM, GDEM, and QDEM) for control
or alarm for high loading or unbalance conditions.
View or Reset Demand Metering Information
The relay shows demand metering quantities and time-stamped peak demand
quantities when you use a communications port or QuickSet to view these quanti-
ties. In addition, you can read the demand and peak demand quantities on the
relay front-panel LCD screen.
To reset the demand metering values use the MET RD command from a commu-
nications terminal, or use the RESET button in the QuickSet HMI > Meter and
Control > Demand/Peak window, or answer
Y and press ENT at the Demand Sub-
menu
reset demand prompt on the front-panel LCD screen. The relay begins the
demand meter sampling period from the time of the demand meter reset.
To reset the peak demand metering values, enter the MET RP command from a
communications terminal, or use the RESET button in the QuickSet HMI > Meter
and Control > Demand/Peak window, or answer
Y and press ENT at the Demand
Submenu
reset peak demand prompt on the front-panel LCD screen. You can also
reset demand metering with Global settings RST_DEM and RST_PDM (for
demand and peak demand) when EDRSTC (Data Reset Control) is Y.
Figure 7.5 Demand Current Logic Outputs
setting EDEM change,
or setting DMTC change
D
e
m
a
n
d
F
u
n
ct
i
on
Thermal
(
EDEM := THM
)
or
Rollin
g
(EDEM := ROL
)
D
e
m
a
n
d
F
u
n
ct
i
on
Thermal
(
EDEM := THM
)
or
Rollin
g
(EDEM := ROL
)
D
e
m
a
n
d
F
u
n
ct
i
on
Thermal
(
EDEM := THM
)
or
Rollin
g
(EDEM := ROL
)
I
A
I
G
(
Residual
)
3I
2
3I
2
(
DEM
)
(
Residual
)
Command
MET RD,
_
+
_
+
m
a
x
.
p
has
e
de
m
a
n
d
cu
rr
e
n
t
Demand
Currents
Relay
Word Bits
Demand Currents
Pickup Settings
I
A
(
DEM
)
I
B
(
DEM)
I
C
(
DEM
)
I
G
(
DEM
)
PDEMP
GDE
MP
_
+
Q
DEM
P
Reset Demand
Reset Demand
Reset Demand
PDEM
GDEM
QDEM
Instantaneous
Currents