Application Note
Measuring and Analyzing the Dielectric Response of Current Transformers Author Stephanie Raetzke |
[email protected] Alan McGuigan| McGuigan|
[email protected] Date August 2011 2011 Related OMICRON Product DIRANA Application Area Current Transformer T ransformer Version v1.0 Document ID ANP_11002_ENU ANP_11002_ENU
Abstract This application guide informs how to measure and analyze the dielectric response of current transformers in order to assess the capacitance, dissipation factor and moisture.
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Content 1
Using this documen documentt ............................................................................ ............................................................................................................. ........................................... .......... 5 1.1 Operator Qualifications and Safety Standards ........................................................................... 5 1.2 Safety Safety measures measures............................................... ................................................................................. ................................................................... ...................................... ..... 5 1.3 Related Related Documents Documents ............................................................... .................................................................................................. ................................................... ................ 5
2
Preparing the Current Transformer ................................................................................................ 5
3
Access and Connections - General Procedure .............................................................................. 6
4
Measure Measurement ment Configu Configuratio rations ns .................................. ................................................................... ................................................................... ...................................... .... 8 4.1 Measurement of HV terminal to bushing capacitor tap ............................................................... 8 4.2 Measurement Measurement of bushing bushing capacitor capacitor tap to housing housing............... ....... ............... .............. .............. ............... ............... .............. ............... ........... ... 8 4.3 Measurement Measurement of HV to secondary secondary or housing with capacitor tap earthed earthed ............... ....... ............... .............. ............. ...... 9
5
Setting Setting up the Software Software............................... .................................................................. .................................................................... ................................................11 ...............11
6
Measure Measurement ments s ............................................................. ............................................................................................... ...................................................................1 .................................12 2 6.1 Pre Measurement Check with the Monitor Device ....................................................................12 6.2 Development of the dissipation factor curve .............................................................................13 6.3 Determination of the Capacitance ............................................................................................14 6.4 Creating Creating a Measure Measurement ment Report Report ............................................................. ..............................................................................................1 .................................14 4 6.5 Measure Measurement ment Errors .............................................................. ................................................................................................... ..................................................15 .............15 6.5.1 6.5.2 6.5.3 6.5.4
Voltage Source Overload Overload ........................................................................................................... 15 Input Overflow Overflow ........................................................................................................................... 15 15 Negative Negative Dissipation Dissipation Factor Factor ........................................................................................................ 15 Disturbances during Time Time Domain Domain Measurement Measurement ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... 16
7
Interpretation of Measurement Data ..............................................................................................17 7.1 Dissipatio Dissipation n factor factor curve..................................................... ....................................................................................... .......................................................17 .....................17 7.2 Frequency dependent capacitance...........................................................................................18 7.3 Moisture Analysis for Instrument Transformers Transformers Using DIRANA............... ........ .............. ............... ............... .............. ............19 .....19
8
Step by step guide for the measurement on current transformer transformers s............... ....... ............... .............. .............. ............... ..........20 ..20
9
Contact Contact Technical Technical Support Support .................................................................. .................................................................................................... ..........................................23 ........23
10 Literatur Literature e .................................................................. ................................................................................................... ................................................................... .....................................23 ...23
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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. product.
OMICRON electronics GmbH including all international branch offices is henceforth r eferred to as OMICRON. © OMICRON 2010. All rights reserved. This application note is a publication of OMICRON. All rights including translation reserved. reserved. Reproduction of any kind, for example, example, photocopying, microfilming, microfilming, optical character recognition and/or storage i n electronic data processing systems, requires t he explicit consent of OMICRON. Reprinting, wholly or in part, is not permitted. The product information, specifications, and technical data embodied in t his 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 i s 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.
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1
Using this document
This application guide provides detailed information on how to measure and to analyze the dielectric response response of current transformers using the OMICRON DIRANA. Please refer to national national and international international safety regulations relevant to working with the DIRANA. The regulation EN 50191 "The Erection and Operation of Electrical Test Equipment" as well as all the applicable regulations for accident prevention in the country and at the site of operation has to be fulfilled.
1.1
Operator Qualifications and Safety Standards
Working on HV devices is extremely dangerous. The measurements described in this Application Guide must be carried out only by qualified, skilled and authorized personnel. Before starting to work, clearly establish the responsibilities. Personnel Personnel receiving training, instructions, directions, or education on t he measurement setup must be under constant supervision of an experienced operator while working with the equipment. The measurement must comply with the relevant national and international safety standards listed below:
EN 50191 (VDE 0104) "Erection and Operation of Electrical Electric al Equipment" EN 50110-1 (VDE 0105 Part 100) "Operation of Electrical Installations" IEEE 510 "Recommended "Recommended Practices for Safety Safety in High-Voltage and High-Power High-Power Testing" Testing" 1910.269(a)(1)(i)(C) 1910.269(a)(1)(i)(C) "Occupationa "Occupationall Safety Safety and and Health Standards Standards - Electric Power Power Generation, Transmission, and Distribution" Appendix C LAPG 1710.6 NASA "Electrical "Electric al Safety"
Moreover, additional relevant laws and internal safety standards may have to be followed.
1.2
Safety measures
Before starting a measurement, read the safety rules in the DIRANA User Manual and observe the application specific safety instructions in this Application Note when performing measurements to protect yourself from high-voltage hazards. hazards.
1.3
Related Documents
DIRANA User Manual – Manual – Contains Contains information on how to use the DIRANA test system and relevant safety instructions.
2
Preparing the Current Transformer
In order to determine the dielectric properties of a current transformer using a dielectric response measurement, the device needs to be de-energized and then disconnected from the network. All connections to the current transformer should be removed in a manner as to conventional dissipation factor tests. If a complete disconnection disconnection is impossible a measure m easurement ment still can be performed. While measuring measuring the capacitance of a CT the Guarding technique prevents disturbing influences by still-connected devices. However, the f ollowing ollowing requirements must be f ulfilled:
Avoid overloadi overloading ng of the instrument due to high currents, e.g. long cables. The remaining devices devices should have low capacitances capacit ances and losses compared to the measured insulation; otherwise high guard currents may cause a negative dissipation factor (p. 15). 15). Avoid electr electromagnetic omagnetic field fiel d coupling since since the remaining devices might act as antenna
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3
Access and Connections - General Procedure
This section gives illustrated introductions how to connect the DIRANA to a current transformer. Please also refer to the t he user manual. 1.
In order to have the same reference potential, connect the grounding cable to the ground terminal on the rear panel of the DIRANA, and clamp its other end to the tank.
2. After this, connect connect the HV conductor conductor to the output channe channell (yellow) of of the DIRANA.
3.
When connecting the measurement cable of the input channel channel (red) to the measurement tap use the split connectors delivered with the DIRANA to connect the tri-axial cable to the connector using alligator clips or wires.
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4.
Connect the guard of both measurement cables to the tank. Confirm a good connection, avoid lacquered surfaces or corroded metal. Clean the surfaces, if necessary. necessary.
5.
If available, wrap a conductive belt around the bushing section, and connect it to the tank.
6. Finally, plug plug the measurement cables into into the DIRANA instrument.
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4
Measurement Configurations
For a CT with a capacitor tap available on the bushing there are three options for dielectric response measurements:
4.1
HV to bushing capacitor tap Bushing capacitor tap to housing HV to housing with capacitor tap earthed
Measurement of HV terminal to bushing capacitor tap
For measuring between the HV connections and the capacitor tap on the bushing section the output is connected to the HV conductor of current transformer. Both HV terminations are connected together without the lead touching the insulator. The earth link is removed from the bushing capacitor tap and the DIRANA output is connected to the HV termination. The input channel CH1 is contacted to the capacitor tap. In the "Configuration" window select "Bushing" test and deselect the measurement at bushing B. Ignore the bridge to the other bushings in the diagram (Figure 1). 1).
Figure 1: DIRANA connection diagram for the measurement of HV terminal to bushing capacitor tap
4.2
Measurement Measurement of bushing capacitor tap to housing
The second measurement is between the capacitor tap of the bushing and the metal housing. In the configuration window select transformer and tick the CL measurement between the secondary winding and the tank (Figure 2). 2). The DIRANA output is connected to the tank and the red measuring lead connected to the capacitor tap with the earth bridge disconnected. Both guards are connected to the HV terminals which are shorted together.
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Figure 2: DIRANA connection diagram for the measurement of bushing capacitor tap to housing
4.3
Measurement Measurement of HV to secondary or housing with capacitor tap earthed
For measurements between the HV terminations and secondary winding or tank select either “Current Transformer” or “Current Transformer with Screen Electrode”. Wiring diagram "Current Transformer" With the “Current Transformer” configuration (Figure 3) the 3) the DIRANA output is connected to the HV t erminals, the input CH1 is connected to the CT secondary with all secondary terminations shorted together. No earth is to be connected to the CT secondary terminations. The guards from the output and measuring leads are connected to the tank. The capacitor tap earth link is closed.
Figure 3: DIRANA connection diagram "Current Transformer"
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Wiring diagram " Current Transformer with Screen Electrode " If the CT has a screen electrode the DIRANA output is connected to the tank and the measuring channel CH1 is connected to the HV terminations (Figure 4). 4). The secondary terminals are shorted together and connected to the tank. No guards are connected. The capacitor tap earth link is closed.
Figure 4: DIRANA connection diagram "Current Transformer with Screen El ectrode"
Please note: If note: If the CT is sand filled the "Moisture Assessment" calculation is not valid for this m easurement. easurement. For such cases comparing to a curve with a known moisture content or condition is the best indication of moisture content levels and the general condition of the CT.
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5
Setting up the Software 1.
Connect DIRANA to a USB port of your laptop and start the DIRANA soft software. ware. The status field in the lower right corner of tthe he main window indicates that the connection is established.
2.
Record all relevant current transformer nameplate data, like serial number number and bushing type. If a moisture analysis should be done, the temperature of the internal insulation is absolutely necessary and should be noted as well. Also record ambient weather conditions.
3.
Press the button "Configure "Confi gure Measurement".
4. By clicking the drop-down-list, drop-down-list, choose the configuration configuration diagram.
5.
Click the "Settings" tab and then enter 1°kHz as start frequency and 10 mHz or 1 mHz as stop frequency. This is sufficient for most current transformers. transformers. Furthermore the measurement measurement mode should be switched to "FDS only" which can be found in "Show Advanced Settings".
6. After this, close the dialog field "Configure "Configure Measurement" Measurement" by clicking clicking on "OK".
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6
Measurements
6.1
Pre Measurement Measurement Check with the t he Monitor Device
Often simple connection problems may affect the measurement. To determine the capacitance, signal-tonoise ratio and noise current for ensuring a successful measurement press the button:
The "PDC Monitor" can be used to estimate the signal-to-noise ratio at different polarization voltages. voltages. Before starting the polarization, the input-coupling noise causes a current, which should be considerably lower (at least 1:10th) than the current after the polarization is started (Figure 5). 5). Recommendations are given in the information box, indicating how to improve t he measurement. measurement.
Figure 5: Pre Measurement check with the PDC Monitor
The dependence of capacitance, tangent delta, power factor or impedance depending on frequency and voltage can be checked using the "FDS Monitor" (Figure 6). 6). The frequency range and the voltage amplitude can be changed using the settings. After applying settings the capacitance, tangent delta, power factor and/or impedance are displayed. They should be stable for a good measurement.
Figure 6: Pre Measurement check using the FDS Monitor
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6.2
Development of the dissipation factor curve
After setting up the the software and and checking the measurement measurement cables, press press the "Send Configuration Configuration to Device and Start Measurement” button . During the running measurement do not move the cables since the piezoelectric effect may cause disturbing charges. The dissipation factor curve will appear, starting at the high frequencies, and developing toward the low frequencies.
Figure 7: Dissipation factor curve starting at the high frequencies
Figure 8: Dissipation factor curve after transition from time to fr equency domain at 0.1 Hz
Figure 9: Complete Dissipation factor curve from 1kHz to 1mHz
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6.3
Determination of the t he Capacitance
Switch to the " c'/c'' Display Mode" to display the real and imaginary part of the capacitance between conductor and measurement tap over frequency as shown in Figure 11. By placing the cursor above the curve pane to the desired frequency, the corresponding absolute capacitance will be displayed in the data view on top.
Figure 10: c'/c" display mode
It is critical to measure the capacitance between the measurement tap and the top of the bushing, since the measurements between the tap terminal and the flange are strongly dependent on external influences like air humidity and dirt. Also, materials like adhesives with higher tan delta are normally used to fix the active part of the bushing against the flange, which are influencing the tan delta.
6.4
Creating a Measurement Report
A measurement measurement report is provided provided by the software, software, containing
dissipation factor curve main measurement information
relevant measurement measurement data like e.g. the dissipation factor and capacitance at power frequency
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For creating a measurement report, select the desired measurements which should be included in the report using the check boxes. The "Print Preview" will now show the measurement report. Use the "Save as/Export" button to save the measurement report as an Excel or PDF f ile.
6.5
Measurement Measurement Errors
6.5.1
Voltage Source Overload
If the instrument is unable to reach the desired voltage, an error message will indicate instrument overload. To solve the problem: Check whether whether the measurement setup has resulted in a short-circuit short-c ircuit.. If capacitive currents cause an over overload load (typical for long cables), decrease the output voltage or start the measurement at lower frequencies than 1000 Hz; i.e. at 100 Hz.
6.5.2
Input Overflow
In case the software displays an input overflow error, check that the CT and the DIRANA have the same reference potential. Usually this error appears when the tank is on a floating potential. Connect the tank to the ground terminal on the rear panel of the DIRANA (p. 6). 6).
6.5.3
Negative Dissipation Factor
The dissipation factor curve may turn negative at high frequencies, see Figure 11. Reasons 11. Reasons for this problem may be at first a high guard impedance, a small measured capacitance in conjunction with a large guard capacitance and high guard currents (dirty bushings). DF 1.000 0.500
CHL
0.100 0.050 0.0100 0.005 0..0 00 01
0..0 01 10
0..1 10 00
1..0 00 00
10..0 00 00
f/Hz
Figure 11: Dielectric measurement with negative dissipation factor
To solve the problem:
Connect all guards of measurement cables and if possible an additional wire from the triaxial connectors at the DIRANA front plate to the tank. Try to decrease the guard currents (clean bushings, disconnect all devices which which are possibly still connected). Confirm a proper connection of of the DIRANA housing to the reference potential is made.
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6.5.4
Disturbances during Time Domain Measurement
Disturbances in the time domain current are transformed into the frequency domain and affect the results displayed in frequency domain (e.g. dissipation factor). Figure 12 shows disturbances on the time domain current for 600-1100 s measurement time as an example. They cause disturbances in dissipation factor for the low frequencies. Generally, the disturbances in time domain will appear in frequency domain depending on their frequency spectrum. DF
I/A
HV+LV to tank
HV+LV to tank
0.0000030
2.000 0.0000020
1.000 0.500 0.200
0.0000010
0.100
0.0000007
0.050
0.0000005 0.020 2
5
10
20
50
10 1 00
200
500 1000
t/s
0.00 0.0010 10
0.01 0.0100 00
0.10 0.1000 00
1.00 1.0000 00
10.0 10.000 000 0
f/Hz
Figure 12: Time domain current with disturbances at around 1000s (left) and its transformation in frequency domain with disturbances at the low frequencies (right). The reason for the disturbances was that guarding was not applicable for this measurement.
To solve this problem:
Use a guarded measurement set-up if possible Apply all all guards of the measurement cables Increase measurement voltage Try to minimize disturbances disturbances by e.g. using using an electrostatic electrostatic shield shield Perform the measurement measurement in frequency frequency domain domain only. In the the dialog field "Configure "Configure Measurement", click on the "Show Advanced Settings" button. Set the "Type of Measurement Sequence" to "FDS only". Please note that this increases the time duration for the measurement substantially.
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7
Interpretation of Measurement Data
7.1
Dissipation factor curve
The dielectric response of instrument transformers has a very specific shape, which is similar to the dielectric response response of cellulosic material itself (Figure 13). 13). The curve has a nearly linear part at the lower frequencies and is rather flat at high frequencies with a minimum around power frequency. 1
DF
1%@20°C
1.000 0.500 3
0.200
0,1
n o i t a p i s s i d
2
0.100
r o t c a f
phase A phase B phase C phase A-2
0,01
0.050 1 0.020 0.010 0.005 0. 001
0. 01
0. 1
1. 0
10. 0
100
0,001
f/Hz
0,01
0,1
1
10
100
1000
frequency in Hz Figure 13: Dielectric response of cellulosic material at 20°C with 1% (2% and 3%) water content
Figure 14: Dielectric response of four current transformers of the same type
Instrument transformers of the same type, which are aged similar and also having a similar water content will have nearly identical curves, like shown in Figure in Figure 14. Ageing 14. Ageing as well as moisture in the solid insulation will increase the dissipation factor especially especially at low frequencies, whereas the dissipation factor at power frequencies is relatively stable. Only for high water contents or strongly aged insulations the dissipation factor will significantly increase at power frequencies. Therefore the 50/60 Hz v alue often only significantly significantly changes, when the ageing or moisture ingress has already led to a bad insulation condition (Figure 15). 15). Since the low fr equencies equencies are much more sensitive to ageing ageing and moisture, it might mi ght be helpful to compare the values e.g. at 10 mHz. The height of the dissipation factor is specific for the voltage class and the type the instrument transformer. Therefore the limits should be defined only within such a group. 10 r o t c a 1 f n o i t a p 0,1 i s s i d
old; 4% 4% water content, content, 9 pS/m oil conductivity conductivity old; 2% 2% water content, 2 pS/ m oil conductivity
0,01 new; 1,2% water content, content, 3 pS/ m oil conductivity conductivity
new; 0,5% water content, content, 6 pS/m oil conductivity conductivity
0,001 0,01
0,1
1
10
100
1000
frequency in Hz Figure 15: Dielectric response of instrument transformers of different age and condition
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7.2
Frequency dependent capacitance
F p n i e1.000 c n a t i c a p a c
old; 4% 4% water w ater content, 9 pS/m oil conductivity old; 2% 2% water w ater content, content, 2 pS/ pS/m m oil conductivity new; 1,2% water content, 3 pS/m oil conductivity
100 0,01
new; 0,5% water content, 6 pS/m oil conductivity
0, 1
1
10
100
1000
frequency in Hz Figure 16: Frequency dependent capacitances of various instrument transformers depending on frequency
The assessment of the frequency dependent capacitance is useful to gain knowledge about the insulation condition. An ideal insulation has a frequency independent capacitance. However, the capacitance of real insulations is increasing at l ow frequencies (Figure 16). 16). For new and dry oil-paper-insulations the increase is very small. For aged and wet insulations the capacitance at low frequencies will increase stronger. This can be visualized by the ratio of the capacitances at very low frequencies, e.g. 10 mHz and power frequency 50/60 Hz. For new and dry insulations this ratio is about 1.05. During t he lifetime the ratio will increase. Most instrument transformers in service with acceptable insulation condition have a ratio of 1.3 or below (Figure 17). 17). This value is rather independent independent of CT type and size. 1,8
z H 0 5
C /
1,6
1,4
z H m 0 1
C
1,2
1,0 0
1
2 3 4 water content in %
5
Figure 17: Ratio of capacitance values between 10 mHz and 50 Hz for vari ous CTs of different insulation condition
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7.3
Moisture Analysis for Instrument Transformers Using DIRANA
The interpretation of the dielectric response in frequency domain for instrument transformers is similar to that of power transformers. Both systems have oil impregnated paper insulations. The difference to the analysis for power transformers lies mainly in the settings for the geometry data. For most instrument transformer geometries, a ratio of 70°% barriers to 30°% oil is suitable. 1.
Select the Measurement
Select the desired measurement in the measurement collection, and open the moisture assessment window by clicking on the "Assessment" button. 2.
Automatic Assessment Press the "Start Assessment" button. The fitting algorithm arranges the parameters of the model (barriers X, spacers Y, oil conductivity, water content) in order to obtain the best fit between the model curve and the measurement curve. If more i nformation is needed, needed, press the "Advanced..." button. Beside moisture content and oil conductivity, conductivity, the v alues for insulation geometry, moisture saturation and bubbling inception temperature can be found here (Figure 18). 18). Also, the measurement results and the fitted model curve are shown here.
Figure 18: Advanced assessment screen after automatic curve fitting
3.
Optimizing the Moisture Analysis by Hand For excellent moisture analysis, a good fitting should be observed. If the ratios for barriers and spacers are not in the usual range, the curve fitting may be not as good as shown in Figure 18. Then the curve fitting needs to be optimized by hand, what can be easily done by using the arrow buttons.
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8
Step by step guide for the measurement on current transformers
Preparation 1.
Use normal operating and safety procedures to access the CT.
2.
Disconnect all external apparatus.
3.
Examine and clean the bushing if needed.
4.
Short both HV terminations terminati ons and short all secondary terminations and connect to earth.
5.
Set up DIRANA instrument in proximity to the CT and extend leads where they will have minimum exposure to casual approaches. If possible keep PC a few meters from DIRANA. Do not approach the CT during a measurement.
6.
Clean HV connection connecti on and earth bar connection locations.
7.
Connect instrument earth and guard leads on earthing points.
Measurement configuration
8. If C1 (HV to cap tap) tap) measurement measurement is required apply DIRANA output (yellow) lead to HV termination. Connect CH1 measuring lead (red) to cap t ap. Connect guards to each clamp. 9.
Select “Monitor” button and check PDC and FDS noise levels.
10. In Configuration Configuration select select "Bushing" "Bushing" measurement measurement in “Connections” tab and deselect bushing b ushing B measurement. 11. In Setting tab select “FDS” as type of measurement . 12. Confirm “Measurement Frequency Range” from 1 kHz to 10 mHz (or 1 mHz for new and dry CTs).
13. Close the “Configuration” window and enter location and name plate details, CT temperature and ambient weather conditions.
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Performing the measurement 14. Confirm CT is clear and start measurement by selecting the
in top tool bar.
15. Confirm that red led on front panel is flashing. 16. Observe the notices notic es in bottom left hand corner of PC screen and the development of the curve plot. 17. If the curve is not regular (please have a look at the 50 Hz values) or error messages are generated use detailed notes to locate the problem. 18. When measurement measurement is completed save the file. Interpretation of measurement data 19. Check the dissipation factor at power frequency frequency and at 10 mHz. 20. Check the increase of capacitance at low frequencies. frequencies. 21. Do an advanced automatic assessment to confirm suitabilit y of of results and curve matching. Additional measurements 22. If C2 (cap tap to tank) and current transformer transformer (overall) measurements measurements are required add additional additional templates. In measurement tab of top toolbar select “Add New Template.. .”. Repeat for second additional measurement.
23. For each measurement in turn select the appropriate Test Type in the “Measurement Configuration > Connections“ tab. Connect output, measuring lead and guards as per diagram for each appropriate selection. Use “Power Tr ansformer – ansformer – 2 Winding” for C2 and select CL measurement only and take HV winding in diagram as CT HV terminations.
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Select either “Current Transformer” or “Current Transformer with Screen Electrode” for full CT test.
"Current Transformer"
"Current Transformer with Screen Electrode"
24. Repeat steps from 9 from 9 to 21. to 21.
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9
Contact Technical Support
In case of further questions, please contact OMICRON's technical technical support: Europe/Middle East/Africa
[email protected] Phone: +43 5523-507-333 Fax: +43 5523-507-7333 North and South America
[email protected] Phone: +1 713 830-4660 or 1 800-OMICRON Fax: +1 713 830-4661 Asia/Pacific
[email protected] Phone: +852 2634 0377 Fax: +852 2634 0390
10
Literature
[1] S. Raetzke, M. K och, M. Krueger, A. Schroecker: "The Assessment of Instrument transformers
by Dielectric Response Response Analysis" TechCon Asia Pacific, Sydney 2011 [2] M. Koch, M. Krüger: “The Negative Dissipation Factor and The Interpretation of the Dielectric Response of Power Transformers" Proceedings of the XVIth International Symposium on High Voltage Engineering, ISH, Cape Town, South Africa, 2009 [3] M. Koch, M. Krüger, S. Tenbohlen: " Comparing Various Moisture Determination Determi nation Methods for Power Transformers" CIGRE Southern Africa Regional Conference, 2009 [4] M. Koch, M. Krüger: “A Fast and Reliable Dielectric Diagnostic Method to Determine Moisture in Power Transformers" Proceedings of the International Conference on Condition Monitoring and Diagnosis CMD, Peking, China, 2008 [5] T. V. Oommen: “Moisture Equilibrium Equilibrium Charts f or Transformer Insulation Insulation Drying Practice” IEEE Transaction on Power Apparatus and Systems, Vol. PAS-103, No. 10, Oct. 1984, pp. 30633067. [6] M. Koch, S. S. Tenbohlen, Tenbohlen, D. Giselbrecht, C. Homagk, T. Leibfried Leibfried: “Onsite, Online and Post Mortem Insulation Diagnostics at Power Transformers”, Transformers”, Cigré SC A2 & D1 Colloquium, Brugge, Belgium 2007 [7] M. Koch, M. Krüger: “Moisture Determination by Improved OnOn-Site Diagnostics”, TechCon Asia
Pacific, Sydney 2008
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OMICRON is 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 i n the area of consulting, commissioning, commissioning, testing, diagnosis, and training make the product range complete. Customers in more than 140 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.
For addresses of OMICRON offices with customer service centers, regional sales offices or offices f or training, consulting and commissioning please visit our web site.
www.omicron.at
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