Fluke 6135A/PMU, Руководство оператора

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6135A/PMU
Operators Manual
3-6
About Synchrophasor Calibration
For a PMU to generate synchrophasors, a PMU must either have its own built in time
reference or take Coordinated Universal Time (UTC) from an external device. UTC is
most commonly obtained from a GPS device and the PMU may receive satellite data
from an aerial. If the PMU does not have an integral GPS receiver, it is provided using
well defined synchronization data such as IRIG-B.
A PMU can be configured for nominal 50 Hz or 60 Hz grids and as Measurement or
Protection devices (M or P). Protection devices control switch gear to automatically
isolate faults. PMU configured as Measurement devices report to a central Phasor Data
Concentrator for off-line monitoring and post event analysis. PMU are configured to
report at specified reporting rates or Frame Rate (FS). In reality, the grid rarely operates
at exactly nominal frequency and contains unwanted distortion components. The PMU
must report Synchrophasors (a time-stamped Phasor) for the voltage and current
fundamental frequency component at the selected reporting rate despite the non-perfect
nature of the input. This means that input filtering is necessary. For the P class, the filter
is fixed irrespective of FS and that some aliasing of distortion will inevitably result is
reflected in the P Class PMU test limits. The rate that an M class PMU reports determines
the anti-aliasing filtering that can be applied and thus the PMU bandwidth.
The mathematical formula for a synchrophasor is:
( )
φ ω
+ =
t Cos X t x
m
) (
The cosine function at the nominal system frequency is synchronized to UTC when
t=0
and
∅ =0
. The Synchrophasor angle is 0 degrees when the maximum of
x(t)
occurs at the
UTC second rollover. The second rollover is known as the 1 PPS (pulse per second) time
signal. See Figure 3-4.
gtu175.emf
Figure 3-4. Synchrophasor Angles