Application Note
Method statement for partial discharge measurement
Author
Dr.-Ing. Kay Rethmeier | kay.rethmeier@omicron.at
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
© OMICRON
Page 1 of 10
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 nonEnglish version, the English version of this note shall govern.
© OMICRON 2010
Page 2 of 10
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:
Test object:
Ck:
CPL542:
MPD600:
USB502:
High voltage filter to suppress noise / interferences from the high voltage source (e.g.
resonance voltage source). Recommended for sources with high interferences
object under test, e.g. cable, transformer,…
Coupling capacitor for decoupling the PD signal.
Measuring impedance for splitting up the voltage and the PD measurement path (incl.
additional protection circuit)
Acquisition unit (measuring channel)
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.
© OMICRON 2010
Page 3 of 10
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
© OMICRON 2010
Page 4 of 10
Figure 4: decoupling through RFCT's at the
cross bonding box
Figure 5: decoupling through RFCT's at the cable
cable screen connection
Figure 6: decoupling with capacitive sensor in the cable joint
© OMICRON 2010
Page 5 of 10
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.
© OMICRON 2010
Page 6 of 10
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 PC’s 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.
© OMICRON 2010
Page 7 of 10
5
Calibration
After setting up the system a calibration of the complete test setup is essential:
> Once the computer has started, double-click the mtronix 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 system’s 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.
Figure 9: mtronix Software, Calibration Tab
© OMICRON 2010
Page 8 of 10
> 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:
> 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.
© OMICRON 2010
Page 9 of 10
OMICRON is an international company serving the electrical power
industry with innovative testing and diagnostic solutions. The application of
OMICRON products provides users with the highest level of confidence in
the condition assessment of primary and secondary equipment on their
systems. Services offered in the area of consulting, commissioning,
testing, diagnosis, and training make the product range complete.
Customers in more than 130 countries rely on the company's ability to
supply leading edge technology of excellent quality. Broad application
knowledge and extraordinary customer support provided by offices in
North America, Europe, South and East Asia, and the Middle East,
together with a worldwide network of distributors and representatives,
make the company a market leader in its sector.
Americas
OMICRON electronics Corp. USA
12 Greenway Plaza, Suite 1510
Houston, TX 77046, USA
Phone: +1 713 830-4660
+1 800-OMICRON
Fax: +1 713 830-4661
info@omicronusa.com
Asia-Pacific
OMICRON electronics Asia Limited
Suite 2006, 20/F, Tower 2
The Gateway, Harbour City
Kowloon, Hong Kong S.A.R.
Phone: +852 2634 0377
Fax: +852 2634 0390
info@asia.omicron.at
For addresses of OMICRON offices with customer service
centers, regional sales offices or offices for training,
consulting and commissioning please visit our web site.
Europe, Middle East, Africa
OMICRON electronics GmbH
Oberes Ried 1
6833 Klaus, Austria
Phone: +43 5523 507-0
Fax: +43 5523 507-999
info@omicron.at
www.omicron.at  www.omicronusa.com