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Metering Function Plus
The Metering Function Plus module
extends the range of metering
functions to include harmonic and
waveform analysis.
Harmonic analysis
The Metering Function Plus module
senses the current and voltage, saves
the measured values, and carries out
a fast Fourier transformation. The result
is the distribution of the harmonics
(in %) up to the 29th harmonic. The
calculated values are made available via
the CubicleBUS and can be displayed via
the PROFIBUS master or the BDA (see
Chapters 3 and 4). They can also be
saved as an Excel-compatible *.csv file
for subsequent diagnosis. On the
ETU776 trip unit, the measured and
calculated values can also be displayed.
The harmonic analysis enables not
only the quality of the network to be
analyzed and logged but also provides
settable alarm levels.
Waveform buffer
The Metering Function Plus module
features two independent waveform
buffers (A and B). Each one has 8
channels, one each for currents I
, I
, and I
, and voltages V
I
c
N
g
a
V
. Each channel is sensed with a
c
frequency of 1,649 kHz and the values
are "pushed" through a shift register
(length: 1 second). The process of
pushing data through the shift register
can be aborted by a configurable
trigger event. Trigger events include
trips, warnings and setpoint alarms
so that the voltage waveform, for
example, can be recorded in the
event of undervoltage tripping.
WL PROFIBUS Communication and Electronic Accessories • July 2004
Communication-capable Circuit Breakers
The Metering Function Plus analyzes the harmonics. This screenshot from the BDA
Figure
shows how the analysis results are displayed.
2-5
, I
,
a
b
, V
, and
b
Metering Function PLUS can record the current waveform. This can be displayed and
Figure
exported using the BDA. A value of trip current is shown here.
2-6
WL Circuit Breaker
2/14
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