I.16
SEL-751 Relay Instruction Manual Date Code 20170927
Synchrophasors
IEEE C37.118 PMU Setting Example
Referring to Table I.10 and Table I.11, it is clear that the lower SPEED
settings are very restrictive.
The smallest practical synchrophasor message would be comprised of one
digital status word, and this message would consume 24 bytes (includes
frequency and DFDT). This type of message could be sent at any message rate
(MRATE = 60) when SPEED := 38400, to MRATE := 5 when SPEED := 2400,
and to MRATE := 1 when SPEED := 600.
Another example application has messages comprised of nine synchrophasors,
one digital status word, and two analog values. This type of message would
consume 68 bytes. The 68-byte message could be sent at any message rate less
than or equal to ten (MRATE) when SPEED := 9600.
Protocol Operation
The SEL-751 only transmits synchrophasor messages over serial ports that
have setting PROTO := PMU. The connected device is typically a
synchrophasor processor, such as the SEL-3373. The synchrophasor processor
controls the PMU functions of the SEL-751, 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.
The SEL-751 does not begin transmitting synchrophasors until an enable
message is received from the synchrophasor processor. The relay stops
synchrophasor transmission when the appropriate command is received from
the synchrophasor processor. The SEL-751 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.
The SEL-751 only responds to configuration block request messages when it
is in the non-transmitting mode.
IEEE C37.118 PMU Setting Example
A utility is upgrading its distribution system to use the SEL-751 for feeder
protection and power-system state measurement. The utility also wants to
install phasor measurement units (PMUs) in each substation to collect data to
monitor voltages and currents throughout the system.
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
Table I.11 Serial Port Bandwidth for Synchrophasors (in Bytes) (Sheet 2 of 2)
Global Setting
MRATE
Port Setting SPEED
300 600 1200 2400 4800 9600 19200 38400 57600
To Next Page
Loading...
