3.29
Date Code 20020903
SEL-587Z Instruction Manual
Relay Elements
Demand Ammetering
Demand Ammetering
The SEL-587Z provides demand and peak demand ammetering for the
following values:
Currents I
A,B,C
Input currents (A primary)
I
G
Residual ground current (A primary;
IG = 3I0 = IA + IB + IC)
3I2
Negative-sequence current (A primary)
The SEL-587Z provides demand ammeters for IA, IB, IC, negative-sequence,
and residual currents. The relay saves time- and date-stamped peak demand
readings for each of the quantities. View this information using the relay front-
panel or serial port
METER D
commands.
Demand Ammeter Settings (DMTC, PDEMP, QDEMP, GDEMP)
The demand ammeters behave much like low-pass filters, responding to
gradual trends in the current magnitude. The relay uses the demand ammeter
time constant setting, DMTC, for all demand ammeter calculations. The time
constant can be set from 5 to 255 minutes. The demand ammeters operate
such that if demand current is reset and a constant input current is applied, the
demand current output will be 90 percent of the constant input current value
DMTC minutes later.
Settable demand ammeter thresholds are available for all three demand
ammeters in units of amps secondary. The thresholds are PDEMP, QDEMP,
and GDEMP for the phase (A, B, and C), negative-sequence, and residual
demand ammeters. If demand currents exceed the set threshold, the respective
Relay Word bit PDEM, QDEM, or GDEM asserts. You can use these Relay
Word bits to alarm for phase overload and negative-sequence or residual
current unbalance for Winding “n.”
Demand
Ammeter
Response
The example in
shows the response of a thermal
demand ammeter 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”).
Summary of Contents for SEL-587Z
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