R.7.2
SEL-421 Relay Reference Manual Date Code 20111215
Synchrophasors
Introduction
The SEL-421 Global settings class contains the synchrophasor settings,
including the choice of synchrophasor protocol and the synchrophasor data set
the relay will transmit. The Port settings class selects which serial port(s) are
reserved for synchrophasor protocol use. See Settings for Synchrophasors on
page R.7.9.
The SEL-421 High-Accuracy Timekeeping function generates status Relay
Word bits and time-quality information that is important for synchrophasor
measurement. Some protection SEL
OGIC variables, and programmable digital
trigger information (C37.118 protocol only) is also added to the Relay Word
bits for synchrophasors—see Synchrophasor Relay Word Bits on page R.7.19.
When synchrophasor measurement is enabled, the SEL-421 creates the
synchrophasor data set at a rate of either 50 or 60 times per second, depending
on the nominal system frequency (Global setting NFREQ). This data set,
including time-of-sample, is available in Analog Quantities in the SEL-421.
See Synchrophasor Analog Quantities on page R.7.20. You can view
synchrophasor data over a serial port set to PROTO := SEL, see View
Synchrophasors by Using the MET PM Command on page R.7.24.
The value of synchrophasor data increases greatly when the data is shared
over a communications network in real time. Two synchrophasor protocols are
available in the SEL-421 that allow for a centralized device to collect data
efficiently from several phasor measurement units (PMUs). Some possible
uses of a system-wide synchrophasor system include the following:
➤ Power-system state measurement
➤ Wide-area network protection and control schemes
➤ Small-signal analysis
➤ Power-system disturbance analysis
Previous SEL-421 relays (firmware version R102 through R111) provided the
SEL Fast Message synchrophasor protocol. SEL-421 relays, beginning with
firmware version R112, still support this protocol, although the required
settings are in a different settings class, and a few message rates are no longer
supported—see SEL-421 Fast Message Synchrophasor Settings on
page R.7.32.
Beginning with firmware version R112, the SEL-421 (and the SEL-421-1)
also support IEEE C37.118, Standard for Synchrophasors for Power Systems.
In the SEL-421, this protocol is referred to simply as C37.118. See Settings
Affect Message Contents on page R.7.26.
In any installation, the SEL-421 can transmit synchrophasors using only one
of the synchrophasor protocols (SEL Fast Message Synchrophasor or
C37.118), as selected by Global setting MFRMT. However, the chosen
protocol is available on multiple serial ports when port setting PROTO :=
PMU and PMUMODE := SERVER.
With either the SEL Fast Message or C37.118 synchrophasor protocol, the
SEL-421 can receive control operation commands over the same channel used
for synchrophasor data transmission. These commands are SEL Fast Operate
messages, which are described in SEL Fast Meter, Fast Operate, and Fast SER
Messages on page R.5.8.
Real-Time Control
You can configure the SEL-421 to receive C37.118 protocol synchrophasor
data. The SEL-421 receives the data over a serial connection and stores these
data in Analog Quantities. Time-alignment is automatic. Use the local phasor
data and as many as two remote sets of phasor data in SEL
OGIC equations.
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