I.2
SEL-751 Relay Instruction Manual Date Code 20170927
Synchrophasors
Synchrophasor Measurement
➤ Small-signal analysis
➤ Power-system disturbance analysis
The SEL-3373 is a Phasor Data Concentrator (PDC) designed to interface
with PMUs, other PDCs, and Synchrophasor Vector Processors (SVPs). The
SEL-3373 has two primary functions. The first is to collect and correlate
synchrophasor data from multiple PMUs. The second is to then compact and
transmit synchrophasor data either to a data historian for post-analysis or to
visualization software for real-time viewing of a power system.
The SEL-3378 Synchrophasor Vector Processor (SVP) is a real-time
synchrophasor programmable logic controller. Use the SVP to collect
synchrophasor messages from relays and phasor measurement units (PMUs).
The SVP time-aligns incoming messages, processes these messages with an
internal logic engine, and sends control command to external devices to
perform user-defined actions. Additionally, the SVP can send calculated or
derived data to devices such as other SVPs, phasor data concentrators (PDCs),
and monitoring systems.
The SEL-751 supports the protocol portion of the IEEE C37.118, Standard for
Synchrophasors for Power Systems. In the SEL-751, this protocol is referred
to as C37.118. See Settings Affect Message Contents on page I.15.
Synchrophasor Measurement
The phasor measurement unit in the SEL-751 measures voltages and currents
on a constant-time basis. These samples are time-stamped with the IRIG time
source. The relay then filters the measured samples according to Global
setting PMAPP := Fast or Narrow (see PMAPP on page I.5).
The phase angle is measured relative to an absolute time reference, which is
represented by a cosine function in Figure I.1. The time-of-day is shown for
the two time marks. The reference is consistent with the phase reference
defined in the C37.118 standard. During steady-state conditions, you can
compare the SEL-751 synchrophasor values directly to values from other
phasor measurement units that conform to C37.118.
Figure I.1 Phase Reference
The TSOK Relay Word bit asserts when the SEL-751 has determined that the
IRIG-B time source has sufficient accuracy and the synchrophasor data meets
the specified accuracy. Synchrophasors are still measured if the time source
threshold is not met, as indicated by Relay Word bit TSOK = logical 0. The
MET PM command is not available in this case.
The instrumentation transformers (PTs or CTs) and the interconnecting cables
can introduce a time shift in the measured signal. Global settings VCOMP,
t
10:00:00:000000 10:00:00:016667
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