GE D90 Plus - Page 565

CHAPTER 11: METERING PHASOR MEASUREMENT UNIT
D90
PLUS
LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL 555
Device Time
Range: time in HH:MM:SS format
Default: 00:00:00
This value reflects the time programmed in the D90
Plus
. This time cannot be modified
from this window.
PMU One-Shot Date
Range: date in MM/DD/YYYY format
Default: 01/01/2007
When the PMU unit one-shot feature is enabled, the D90
Plus
continuously compares the
device date with this value.
PMU One-Shot Time
Range: time in HH:MM:SS format
Default: 00:00:00
When the PMU one-shot feature is enabled, the D90
Plus
continuously compares the
device date with this value.
Manual Date
Range: date in MM/DD/YYYY format
Default: 01/01/2007
The
PMU One-Shot Date is updated to the value specified by this setting when the Set
PMU One-Shot Date and Time command is executed.
Manual Time
Range: time in HH:MM:SS format
Default: 00:00:00
The
PMU One-Shot Time is updated to the value specified by this setting when the Set
PMU One-Shot Date and Time command is executed.
Testing accuracy of the Phasor Measurement Unit
The Phasor Measurement Unit one-shot feature can be used to test accuracy of the
synchrophasor measurement. GPS-synchronized test sets perform a similar function;
instead of measuring the phasor from physical signals with respect to the externally
provided time reference, they produce the physical signals with respect to the externally
provided time reference, given the desired phasor values. Therefore the GPS-synchronized
test sets cannot be assumed more accurate than the PMUs under test. This calls for a
method to verify both the measuring device (PMU) and the source of signal (test set).
With reference to the following figure, the one-shot feature can be configured to trigger a
high-accuracy scope to capture both the time reference signal (rising edge of the 1 pps
signal of the IRIG-B time reference), and the measured waveform. The high-accuracy high-
sampling rate record of the two signals captured by the scope can be processed using
digital tools to verify the magnitude and phase angle with respect to the time reference
signal. As both the time reference and the measured signals are raw inputs to the PMU
under test, their independently captured record, processed using third-party software, is a
good reference point for accuracy calculations. Such a record proves useful when
discussing the test results, and can be retained as a part of the testing documentation.
Note that the PMU under test does not have to be connected to a real GPS receiver as the
accuracy is measured with respect to the timing reference provided to the PMU and not to
the absolute UTC time. A simple IRIG-B generator can be used instead. Also, the test set
does not have to support GPS synchronization. Any stable signal source can be used. If
both the PMU under test and the test set use the timing reference, they need to be driven
from the same IRIG-B signal: either the same GPS receiver or IRIG-B generator. Otherwise,
do not compare the setpoints of the test set and the PMU measurements because they are
referenced to different time scales.