Schweitzer Engineering SEL-387-0, Instruction Manual, Page: 177 / 556

5.3
Date Code 20170601 Instruction Manual SEL-387-0, -5, -6 Relay
Metering and Monitoring
Metering Functions
and NDEM n P is compared to the residual demand. Relay Word bits PDEM n ,
QDEM n , or NDEM n 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 DATC
n 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:
Equation 5.1
The next function, the peak demand ammeter function, keeps track of the
greatest 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 winding, i.e., the largest of the phase current
demands, the negative-sequence demand, and the residual demand, against
registers containing the greatest demand value of each type since the last reset
of the registers. This is done 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 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 primary amperes. If the command is typed as
MET P m ,
where m is any number from 1 to 32767, the report will be repeated m times in
succession. In this mode, subsequent reports are not generated until the
previous report has been completely sent. The format for the
MET P report is
as follows:
=> METER P <Enter>
XFMR 1 Date: MM/DD/YY Time: HH:MM:SS.SSS
STATION A
Peak Dem I (A, pri) Date: Time:
Wdg 1 IAW1 12345 MM/DD/YY HH:MM:SS.SSS
IBW1 12345 MM/DD/YY HH:MM:SS.SSS
ICW1 12345 MM/DD/YY HH:MM:SS.SSS
3I2W1 12345 MM/DD/YY HH:MM:SS.SSS
IRW1 12345 MM/DD/YY HH:MM:SS.SSS
Wdg 2 IAW2 12345 MM/DD/YY HH:MM:SS.SSS
IBW2 12345 MM/DD/YY HH:MM:SS.SSS
ICW2 12345 MM/DD/YY HH:MM:SS.SSS
3I2W2 12345 MM/DD/YY HH:MM:SS.SSS
IRW2 12345 MM/DD/YY HH:MM:SS.SSS
Wdg 3 IAW3 12345 MM/DD/YY HH:MM:SS.SSS
IBW3 12345 MM/DD/YY HH:MM:SS.SSS
ICW3 12345 MM/DD/YY HH:MM:SS.SSS
3I2W3 12345 MM/DD/YY HH:MM:SS.SSS
IRW3 12345 MM/DD/YY HH:MM:SS.SSS
Wdg 4 IAW4 12345 MM/DD/YY HH:MM:SS.SSS
IBW4 12345 MM/DD/YY HH:MM:SS.SSS
ICW4 12345 MM/DD/YY HH:MM:SS.SSS
3I2W4 12345 MM/DD/YY HH:MM:SS.SSS
IRW4 12345 MM/DD/YY HH:MM:SS.SSS
LAST PEAK 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
Wdg4: MM/DD/YY HH:MM:SS.SSS
Id(t) I
NEW
Id
0
I
NEW
–
 
e
10
 
ln
 
t
DATCn
--------------------- • –
• + =