R.7.28
SEL-421 Relay Reference Manual Date Code 20111215
Synchrophasors
C37.118 Synchrophasor Protocol
The SEL-421 will only respond to configuration block request messages when
it is in the non-transmitting mode.
Independent Ports
Each serial port with the PROTO := PMU setting is independently configured
and enabled for synchrophasor and Fast Operate commands. For example, if
there are two serial ports set to PROTO := PMU, the status of one port has no
effect on the other port. One port might be commanded to start transmitting
synchrophasor messages, while the other port is idle, responding to a
configuration block or Fast Operate request, or transmitting synchrophasors.
The ports are not required to have the same SPEED setting, although the
slowest SPEED setting on a PROTO := PMU port will affect the maximum
Global MRATE setting that can be used.
PMU Setting Example
A power utility is upgrading the line protection on its 230 kV system to use
the SEL-421 Relay as main protection. The grid operator also wants the utility
to install phasor measurement units (PMUs) in each 230 kV substation to
collect data for a new remedial action scheme, and to eventually replace their
present state-estimation system.
The PMU data collection requirements call for the following data, collected at
10 messages per second:
➤ Frequency
➤ Positive-sequence voltage from the bus in each substation
➤ Three-phase and positive-sequence current for each line
terminal
➤ Indication when the line breaker is open
➤ Indication when the voltage or frequency information is
unusable
➤ Ambient temperature (one reading per station)
➤ Station battery voltage
➤ No relay control from the PMU communications port, for the
initial stage of the project
The utility is able to meet the grid operator requirements with the SEL-421, an
SEL-2600A RTD Module, an SEL-2407 Satellite Synchronized Clock, and an
SEL-3306 Synchrophasor Processor in each substation.
This example will cover the PMU settings in one of the SEL-421 relays.
Some system details:
➤ The nominal frequency is 60 Hz.
➤ The line is protected by a breaker-and-a-half scheme (similar to
Figure 1.7 on page R.1.10).
➤ The station ambient temperature is collected by an SEL-2600A,
channel RTD01.
➤ The line pts and wiring have a phase error of 4.20 degrees
(lagging) at 60 Hz.
➤ The breaker 1 cts and wiring have a phase error of 3.50 degrees
(lagging) at 60 Hz.
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