R.7.27
Date Code 20111215 Reference Manual SEL-421 Relay
Synchrophasors
C37.118 Synchrophasor Protocol
Referring to Table 7.15 and Table 7.16, it is clear that the lower SPEED
settings are very restrictive.
The smallest practical synchrophasor message would be comprised of one
synchrophasor and one digital status word, and this message would consume
between 26 and 34 bytes, depending on the numeric format settings. This type
of message could be sent at any message rate (MRATE) when
SPEED := 38400 or 57600, up to MRATE := 50 or 30 when SPEED := 19200,
and up to MRATE := 25 or 20 when SPEED := 9600.
Another example application has messages comprised of eight
synchrophasors, one digital status word, and two analog values. This type of
message would consume between 62 and 98 bytes, depending on the numeric
format settings. The 62-byte version, using integer numeric representation,
could be sent at any message rate (MRATE) when SPEED := 57600. The
98-byte version, using floating-point numeric representation, could be sent at
up to MRATE := 30 when SPEED := 57600, up to MRATE := 25 when
SPEED := 38400, and up to MRATE := 12 when SPEED := 19200.
Protocol Operation
The SEL-421 will only transmit synchrophasor messages over serial ports that
have setting PROTO := PMU. The connected device will typically be a
synchrophasor processor, such as the SEL-3306. The synchrophasor processor
controls the PMU functions of the SEL-421, with IEEE C37.118 commands,
including commands to start and stop synchrophasor data transmission, and
commands to request a configuration block from the relay, so the
synchrophasor processor can automatically build a database structure.
Transmit Mode Control
The SEL-421 will not begin transmitting synchrophasors until an enable
message is received from the synchrophasor processor. The relay will stop
synchrophasor transmission when the appropriate command is received from
the synchrophasor processor. The SEL-421 can also indicate when a
configuration change occurs, so the synchrophasor processor can request a
new configuration block and keep its database up-to-date.
Table 7.16 Serial Port Bandwidth for Synchrophasors (in Bytes)
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
30 (60 Hz only) 22 45 90 136
50 (50 Hz only) 27 54 81
60 (60 Hz only) 22 45 68
To Next Page
Loading...
