Date Code 20170927 Instruction Manual SEL-751 Relay
Appendix I
Synchrophasors
Overview
The SEL-751 Relay provides Phasor Measurement Unit (PMU) capabilities
when connected to an IRIG-B time source with an accuracy of ±10 µs or
better. Synchrophasor data are available via the MET PM ASCII command
and the C37.118 Protocol.
Synchrophasor measurement refers to the concept of providing measurements
taken on a synchronized schedule in multiple locations. A high-accuracy
clock, commonly called a Global Positioning System (GPS) receiver, such as
the SEL-2407 Satellite-Synchronized Clock, makes synchrophasor
measurement possible.
The availability of an accurate time reference over a large geographic area
allows multiple devices, such as SEL-751 Relays, to synchronize the
gathering of power system data. The accurate clock allows precise event
report triggering and other off-line analysis functions. Synchrophasors are still
measured if the high-accuracy time source is not connected; however, the data
are not time-synchronized to any external reference, as indicated by Relay
Word bits TSOK := logical 0 and PMDOK := logical 0.
The SEL-751 Global settings class contains the synchrophasor settings,
including the choice of transmitted synchrophasor data set. The Port settings
class selects which serial port(s) or Ethernet port you can use for
synchrophasor protocol. See Settings for Synchrophasors on page I.4.
The SEL-751 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 is also added to the Relay Word bits for synchrophasors. See
Synchrophasor Relay Word Bits on page I.11.
When synchrophasor measurement is enabled, the SEL-751 creates the
synchrophasor data set at a user-defined rate. Synchrophasor data are available
in ASCII format over a serial port set to PROTO = SEL. See View
Synchrophasors Using the MET PM Command on page I.13.
The value of synchrophasor data increases greatly when you can share the
data over a communications network in real time. A synchrophasor protocol is
available in the SEL-751 that allows 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
➤ Generator Model Validation
➤ Wide-area network protection and control schemes
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