Sel SEL-421 - Settings Affect Message Contents; Communications Bandwidth; Size of a C37.118 Synchrophasor Message

R.7.26
SEL-421 Relay Reference Manual Date Code 20111215
Synchrophasors
C37.118 Synchrophasor Protocol
Settings Affect
Message Contents
The SEL-421 allows several options for transmitting synchrophasor data.
These are controlled by Global settings described in Settings for
Synchrophasors on page R.7.9. You can select how often to transmit the
synchrophasor messages (MRATE), which synchrophasors to transmit
(PHDATAV, PHDATAI, and PHCURR), which numeric representation to use
(PHNR), and which coordinate system to use (PHFMT).
The SEL-421 automatically includes the frequency and rate-of-change-of-
frequency in the synchrophasor messages. Global setting FNR selects the
numeric format to use for these two quantities.
The relay can include up to eight user-programmable analog values in the
synchrophasor message, as controlled by Global setting NUMANA, and 0, 16,
or 32 digital status values, as controlled by Global setting NUMDSW.
The SEL-421 always includes the results of four synchrophasor trigger reason
SEL
OGIC equations TREA1, TREA2, TREA3, and TREA4, and the trigger
SEL
OGIC equation result PMTRIG, in the synchrophasor message.
Communications
Bandwidth
A phasor measurement unit (PMU) that is configured to transmit a single
synchrophasor (positive-sequence voltage, for example) at a message rate of
once per second places little burden on the communications channel. As more
synchrophasors, 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 SEL-421 or SEL-5030 software
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
programmable digital data will add to the byte requirements. Table 7.15 can
be used to calculate the number of bytes in a synchrophasor message.
Tab le 7.16 lists the baud settings available on any SEL-421 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 7.15 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 0, 1, 2, 3, 4, 5,
6, 8, 9, or 12
4 {PHNR := I}
8 {PHNR := F}
096
Frequency 2 (fixed) 2 {FNR := I}
4 {FNR := F}
48
Analog Values 0 – 8 4 0 32
Digital Status
Words
0 – 2204
Total (Minimum and Maximum) 22 158