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OMICRON Page 1 of 11
Application Note
Method statement for partial discharge measurement
Author Dr.-Ing. Kay Rethmeier | [email protected] Date
Oct, 2007
Related OMICRON Product CAL 542, MPD 600, MCU 502
Application Area Partial Discharge Measurements
Version v1.0
Document ID ANP_10036_ENU
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Content
1 Principle measurement cicuit
...............................................................................................................3
2 Connection (decoupling) possibilities
................................................................................................4
3 Test equipment
......................................................................................................................................6
4 Test procedure
.......................................................................................................................................7
5 Calibration
..............................................................................................................................................8
6 Measurement
..........................................................................................................................................9
Please use this note only in combination with the related
product manual which contains several important safety
instructions. The user is responsible for every application that
makes use of an OMICRON product. OMICRON electronics GmbH including
all international branch offices is henceforth referred to as
OMICRON. OMICRON 2010. All rights reserved. This application note
is a publication of OMICRON.
All rights including translation reserved. Reproduction of any
kind, for example, photocopying, microfilming, optical character
recognition and/or storage in electronic data processing systems,
requires the explicit consent of OMICRON. Reprinting, wholly or in
part, is not permitted.
The product information, specifications, and technical data
embodied in this application note represent the technical status at
the time of writing and are subject to change without prior
notice.
We have done our best to ensure that the information given in
this application note is useful, accurate and entirely reliable.
However, OMICRON does not assume responsibility for any
inaccuracies which may be present. OMICRON translates this
application note from the source language English into a number of
other languages. Any translation of this document is done for local
requirements, and in the event of a dispute between the English and
a non-English version, the English version of this note shall
govern.
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OMICRON 2013 Page 3 of 11
1 Principle measurement cicuit The principle measurement circuit
is described in the block diagram below. The coupling capacitor Ck
is only one possibility to decouple the PD signal. Other ways of
decoupling are shown in chapter 2.
Figure 1: principle measurement circuit
HV filter: High voltage filter to suppress noise / interferences
from the high voltage source (e.g. resonance voltage source).
Recommended for sources with high interferences
Test object: object under test, e.g. cable, transformer, Ck:
Coupling capacitor for decoupling the PD signal. CPL542: Measuring
impedance for splitting up the voltage and the PD measurement path
(incl.
additional protection circuit) MPD600: Acquisition unit
(measuring channel) USB502: fiber optical controller The
connection(s) between the test object and the acquisition unit MPD
600 should be as short as possible to reduce unwanted interference.
The length of the connection between the MPD 600 and the USB 502
can be as long as necessary (up to 2 km) because no additional
interferences will be added due to the fiber optical transmission.
If more than one measurement is needed, the channels can be easily
cascaded via the optical bus.
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OMICRON 2013 Page 4 of 11
2 Connection (decoupling) possibilities The decoupling of the PD
signal can be done on different ways depending on the test object
and the onsite conditions. The most common ways are shown in the
pictures below:
Figure 2: connection to capacitive measurement taps of the
transformer
Figure 3: connection through coupling capacitors
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OMICRON 2013 Page 5 of 11
Figure 4: decoupling through RFCT's at the Figure 5: decoupling
through RFCT's at the cable cross bonding box cable screen
connection
Figure 6: decoupling with capacitive sensor in the cable
joint
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3 Test equipment Beside the decoupling equipment mentioned
before, following items are necessary to perform the PD test:
Figure 7: MPD 600 test equipment
The charge range of the calibrator has to be selected in the
range of the expected (allowed) charge level for the test
object.
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4 Test procedure
Figure 8: Test procedure
Preparation: The prior information about the test object is
necessary to select the right measurement equipment (calibrator,
quadripole/measuring impedance, fiber optical cable length). The
system will be set up the following way:
> Connect the fiber optics controller to the Notebook
Computer using a standard USB cable (USB 2.0).
> Connect the MPD 600 Acquisition unit to the fiber optics
controller using fiber optical cables.
See wiring diagram on next page for details. Please observe that
TX (transmit) is always
connected to RX (receive) and vice versa.
> Connect the power supply (or battery) to the MPD 600
Acquisition unit. The red LED starts flashing indicating that the
acquisition unit is ready for operation.
> Connect the external coupling unit CPL 542, also referred
to as quadripole or measuring impedance.
Use two short BNC cables and connect the PD and V outputs of the
coupling unit
CPL 542 to the PD and V inputs of the acquisition unit MPD
600.
> Connect the coupling unit CPL 542 to a high voltage
coupling capacitor (or RFCT, measuring tap,
other Sensor). Always remember to keep the cable(s) as short as
possible.
> Connect the Notebook PCs power supply and switch it on.
Perform test: Select an appropriate measurement frequency and
bandwidth (in the range of the applicable measurement standard).
This is to optimize the signal to noise ratio and to reduce
external interferences. In case of high external disturbances a
gaiting channel with antenna can be connected to the measuring
system. The "perform test" steps are described in the next
chapters. Reporting/assessment The reporting will be done based on
the stored data. This can be done either with the exported graphics
or with the stored data stream.
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5 Calibration After setting up the system a calibration of the
complete test setup is essential:
> Once the computer has started, double-click the Omicron
Icon to start the software:
> Use the mouse or keyboard to select the main menu item Mode
in the top menu bar. Then
select Basic for the systems operating mode.
> Make sure that the Settings tab is selected. Find the combo
box labeled Trigger source and
select unit1.1 as the trigger source. If you are performing a
calibration you may also select line
as trigger source. The system then uses a light-sensitive sensor
to synchronize itself to
fluorescent light sources. Do not forget to change the trigger
source back to unit 1.1 before
performing the actual measurement.
> Select the fCenter (center frequency) box and enter a value
of 350 kHz.
> Select a bandwidth of 300 kHz. This center frequency and
bandwidth configuration sets up the
measurement system for an IEC 602 70-compliant measurement.
Other settings might be
necessary to receive a better signal to noise ration
> Make sure that the Input Protection option is checked. You
may uncheck this option for very
sensitive measurements but the PD input of the acquisition unit
is then somewhat more sensitive
to damage by electrical surges.
> Go to the Settings tab. For Mode select Unipolar
Logarithmic.
> Set QMax (maximum charge displayed) to 1 nC.
> Set QMin (minimum charge registered and displayed) to 1
pC.
> Optionally, check the Show individual PD events option.
Individual PD events will then be shown
as phase and amplitude resolved spikes in real time. Now change
to the calibration settings by selecting the Calibration tab.
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OMICRON 2013 Page 9 of 11
Figure 9: Omicron Software, Calibration Tab
> Uncheck the Enable test generator option.
> Check the External quadripole configuration option.
Connect the calibrator to the test object. Select a charge of
100 pC. Pulses should clearly extend from the background noise as
spikes. If the noise floor covers PD pulses, select a higher charge
on the calibrator (depending on your test object and available
charge calibrator you may use another charge level).
> Enter the calibrator charge (e.g. 100 pC) into the
Calibrate to field in the PD section.
> Click on the Compute button in the PD section. The display
value for QIEC should now
correspond to the calibrator charge. Now the charge value is
calibrated. The second step is to calibrate the test voltage
value:
> Disconnect the calibrator.
> Secure the high voltage test set-up observing safety
procedures.
> Turn on the high-voltage supply. Set voltage to a known
level (e.g. 2 kV).
> Enter voltage level (e.g. 2 kV) into the Calibrate to field
in the Voltage section.
> Click on the Compute button in the voltage section. The
display value for voltage should now
correspond to the actual voltage.
6 Measurement After the calibration is finished, the PD
measurement can take place. The measurement should be performed
according to the applicable standard for this type of test and test
object. Main issues of the standards are test voltage levels, test
duration and maximum PD levels. To get a so called "pattern" of the
partial discharge, the creation of a histogram is useful:
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OMICRON 2013 Page 10 of 11
> Start the test voltage run (of the test voltage source)
> Click on the Go button in the "Settings" tab. A histogram
will be accumulated over a specified
time period. The progress bar at the bottom will indicate the
progress of this operation.
> Once a histogram has been accumulated, the image may be
saved to disk by right-clicking on the
scope display. A context-menu will pop up and offer to save the
image to disk as a PNG file. PNG
is a popular image format providing lossless compression.
> All of the data gathered during a measurement may be
recorded for later analysis by clicking on
the Record button (marked by a large red dot). The software will
display the hard disk space
consumed during this operation and the remaining disk space. The
stored data can be used afterwards to assess the test object, to
create a test report and to give recommendations.
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OMICRON is an international company serving the electrical
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application of
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consulting and commissioning please visit our web site.
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