Schweitzer Engineering Laboratories SEL-351A, Manual

Page: 651 / 666

L.3
Date Code 20080213
Instruction Manual SEL-351A Relay
SEL Synchrophasors
Synchrophasor Measurement
Synchrophasor Measurement
The phasor measurement unit in the SEL-351A measures three voltages and
three currents at each one-second instant, as determined by the IRIG-B time
source. The phase angle is measured relative to an absolute reference, which is
represented by a cosine function in
Figure L.1 . The reference is consistent
with the phase reference defined in the C37.118 standard. During steady-state
conditions, the SEL-351A synchrophasor values can be directly compared to
values from other phasor measurement units that conform to C37.118.
Synchrophasor values are available for the full frequency range of the
SEL-351A.
Figure L.1 Phase Reference
The TSOK Relay Word bit asserts when the SEL-351A 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.
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