Date Code 20020129
Metering and Monitoring
5-3
SEL-387E Instruction Manual
=>>METER D<ENTER>
XFMR 1 Date: MM/DD/YY Time: HH:MM:SS.SSS
STATION A
Phase Currents Sequence Currents
Wdg1 IAW1 IBW1 ICW1 3I2W1 IRW1
Dem I (A,pri) 12345 12345 12345 12345 12345
Wdg2 IAW2 IBW2 ICW2 3I2W2 IRW2
Dem I (A,pri) 12345 12345 12345 12345 12345
Wdg3 IAW3 IBW3 ICW3 3I2W3 IRW3
Dem I (A,pri) 12345 12345 12345 12345 12345
LAST DEMAND RESET FOR Wdg1: mm/dd/yy hh:mm:ss.sss
Wdg2: mm/dd/yy hh:mm:ss.sss
Wdg3: mm/dd/yy hh:mm:ss.sss
=>>
The most recent demand resets for each winding are shown in the METER D report.
The demand ammeter function simulates the long-term heating effects of current at a particular
level by accumulating the demand current on an exponential basis, using a thermal time constant
setting, DATCn, for each winding (n = 1, 2, 3). DATCn can be set over a range of 5 to 255
minutes (4 hours 15 minutes). The demand values in secondary amperes are compared to user-
defined thresholds, PDEMnP, QDEMnP, and NDEMnP. PDEMnP is compared to the largest of
the three individual phase current demands for Winding n, while QDEMnP is compared to the
negative-sequence demand, and NDEMnP is compared to the residual demand. Relay Word bits
PDEMn, QDEMn, or NDEMn are asserted if the appropriate demand exceeds the stated
threshold. These bits can be used to initiate a display or to close an output contact for alarming
or tripping purposes.
The demand ammeter output for a step change in current of S amperes is a smoothly rising
exponential that produces a demand change of 0.9 times S at time DATCn after the step change
occurred (see Figure 5.1). For example, if the demand current has stabilized at some value Id
0
before time zero and at t = 0 the current suddenly jumps to a new value I
NEW
, the demand current
as a function of time will have the equation:
(
)
( )
[
]
DATCn
/
t
10
ln
NEW
0
NEW
e
•
I
Id
I
)
t
(
Id
-
-
-
+
=
The next function, the peak demand ammeter function, keeps track of the largest value of Id(t)
since the last reset of the peak demand registers.
Peak Demand Ammeter Function (METER P Command)
The peak demand ammeter function compares the value of the demand ammeter outputs for each
current winding, i.e., the largest of the phase current demands, the negative-sequence demand,
and the residual demand, against registers containing the largest demand value of each type since
the last reset of the registers. This happens every two seconds. If the particular Id(t) exceeds the
register value, it replaces the value in the register and becomes the new peak value. These peak
values are time and date stamped.
In response to the
METER P
(
MET P
) command, the phase current peak demands, as well as
the negative-sequence and residual current peak demands for each winding, are displayed in