Schweitzer Engineering Laboratories SEL-421-4 - Page 1430

18.24
SEL-400 Series Relays Instruction Manual Date Code 20171006
Synchrophasors
C37.118 Synchrophasor Protocol
Communications Bandwidth
A phasor measurement unit (PMU) that is configured to transmit a single syn-
chrophasor (positive-sequence voltage, for example) at a message rate of once
per second places little burden on the communications channel. As more syn-
chrophasors, analog values, or digital status words are added, or if the message
rate is increased, some communications channel restrictions come into play.
If the SPEED setting on any serial port set with PROTO := PMU is insufficient
for the PMU Global settings, the relay or QuickSet will display an error message
and fail to save settings until the error is corrected.
The C37.118 synchrophasor message format always includes 16 bytes for the
message header and terminal ID, time information, and status bits. The selection
of synchrophasor data, numeric format, programmable analog, and programma-
ble digital data will add to the byte requirements. Table 18.13 can be used to cal-
culate the number of bytes in a synchrophasor message.
Table 18.14 lists the bps settings available on any relay serial port (setting
SPEED), and the maximum message size that can fit within the port bandwidth.
Blank entries indicate bandwidths of less than 20 bytes.
Table 18.13 Size of a C37.118 Synchrophasor Message
Item
Possible
number of
quantities
Bytes per
quantity
Minimum
number of
bytes
Maximum
number of
bytes
Fixed 18 18
Synchrophasors
a
a
Some SEL relays have a smaller number of possible synchrophasors.
0, 1, 2…32 4 (PHNR := I)
8 (PHNR := F)
0256
Frequency 2 (fixed) 2 (FNR := I)
4 (FNR := F)
48
Analog Values 0 – 16 4 0 64
Digital Status Words 0 – 4 2 0 8
Total (Minimum and Maximum) 22 354
Table 18.14 Serial Port Bandwidth for Synchrophasors (in Bytes) (Sheet 1 of 2)
Global Setting
MRATE
Port Setting SPEED
300 600 1200 2400 4800 9600 19200 38400 57600
1 21 42 85 170 340 680 1360 2720 4080
2 21 42 85 170 340 680 1360 2040
4 (60 Hz only) 21 42 85 170 340 680 1020
5 34 68 136 272 544 816
10 34 68 136 272 408
12 (60 Hz only) 28 56 113 226 340
15 (60 Hz only) 21 45 90 181 272
20 (60 Hz only) 34 68 136 204
25 (50 Hz only) 27 54 108 163