For years, electric utility transmission thermographers have wanted a camera that could spot leaking sulfur hexafluoride, SF6. As an insulating gas, SF6 is widely used by the electric power industry in high voltage circuit breakers to prevent arcing. Early efforts met with limited success through the use of imagers that required active scanning with infrared lasers. The resulting systems were somewhat cumbersome and required specific conditions which limited their utility. Now there is an IR camera that can spot SF6 in very small amounts and is a completely passive system, requiring no infrared laser but for the smallest leaks. This paper gives a brief history of SF6 as an insulating gas, problems caused by leaking SF6, the theory behind the IR camera, and why it works as well as it does. Additionally, we present some sample findings from both the laboratory and actual operating circuit breakers in high voltage systems that use SF6.
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Discussion welcomed.
Sunday, November 30, 2008
A Novel, Compact Instrument for the Measurement and Evaluation of Relaxation Currents conceived for On-Site Diagnosis of Electric Power Apparatus
A Novel, Compact Instrument for the Measurement and Evaluation of Relaxation Currents conceived for On-Site Diagnosis of Electric Power Apparatus
Abstract: Ageing of insulation materials and systems may well be detected by quantitative measurements of their dielectric response. Such measurements can be performed in the frequency or time domain. In this contribution, a novel type of equipment based on relaxation current measurements is introduced which is designed for on-site tests of high voltage power apparatus. The Introduction outlines the reasons for the development. Then, the technique of the instrument is briefly explained. Finally, some examples of on-site measurements on power transformers are presented and post-processing and interpretation of the results is demonstrated.
The measurements presented in this paper have been carried out in due course of the project "Insulation diagnosis of power transformers", performed at the High Voltage Laboratory of the Swiss Federal Institute of Technology [12]. This project was financially supported from "Projekt und Studienfonds der Elektrizitätswirtschaft" (PSEL Project No. 65).
View full paper from Alff
Discussion welcomed.
Abstract: Ageing of insulation materials and systems may well be detected by quantitative measurements of their dielectric response. Such measurements can be performed in the frequency or time domain. In this contribution, a novel type of equipment based on relaxation current measurements is introduced which is designed for on-site tests of high voltage power apparatus. The Introduction outlines the reasons for the development. Then, the technique of the instrument is briefly explained. Finally, some examples of on-site measurements on power transformers are presented and post-processing and interpretation of the results is demonstrated.
The measurements presented in this paper have been carried out in due course of the project "Insulation diagnosis of power transformers", performed at the High Voltage Laboratory of the Swiss Federal Institute of Technology [12]. This project was financially supported from "Projekt und Studienfonds der Elektrizitätswirtschaft" (PSEL Project No. 65).
View full paper from Alff
Discussion welcomed.
Low voltage short circuit impedance measurement
Low voltage short-circuit impedance measurement
The low voltage short -circuit impedance measurement by means of a low voltage three phase power source can be performed because the impedance valuedoes not depend on the applied voltage.The low voltage short-circuit impedance measurement requires utilization of highly accurate instrumentation on the one side, and elimination of the errors caused by the fluctuations of low voltage power networks due to welding equipment, etc., on the other.In order to carry out these measurements a diagram developed. The diagram uses data acquisition and processing system (DAQ) that enables evaluation of the measured data, the short-circuitimpedance variation curve plotting on the spot, as well as the subsequent processing obtained data. The processing system also corrects the data with the supplyvoltage frequency variation.
Furthermore:
The short-circuit impedance measurement between allthe winding pairs and by each position of the on-load tapchanger is imperiously necessary for:
- verifying the observance of the technical conditions,the designed ones included;
- verifying the possible nonconformities in thewinding manufacturing;
- verifying the behavior of the winding operation onsite (the measurement is performed in agreement with thenorms in force);
- carrying out the system calculations and the short circuitones (including the correct protection regulation);
- verifying the loading of the same type, as well as a of different type transformer units.
The short-circuit impedance measurement can beperformed by connecting the measurement installation to a low voltage (380/220V) source provided that highly accurate instrumentation enabling the automatic data processing is used.
Taken from a paper:
Power Transformer Units Condition Assessment Using VirtualInstrumentation
Discussion welcomed.
The low voltage short -circuit impedance measurement by means of a low voltage three phase power source can be performed because the impedance valuedoes not depend on the applied voltage.The low voltage short-circuit impedance measurement requires utilization of highly accurate instrumentation on the one side, and elimination of the errors caused by the fluctuations of low voltage power networks due to welding equipment, etc., on the other.In order to carry out these measurements a diagram developed. The diagram uses data acquisition and processing system (DAQ) that enables evaluation of the measured data, the short-circuitimpedance variation curve plotting on the spot, as well as the subsequent processing obtained data. The processing system also corrects the data with the supplyvoltage frequency variation.
Furthermore:
The short-circuit impedance measurement between allthe winding pairs and by each position of the on-load tapchanger is imperiously necessary for:
- verifying the observance of the technical conditions,the designed ones included;
- verifying the possible nonconformities in thewinding manufacturing;
- verifying the behavior of the winding operation onsite (the measurement is performed in agreement with thenorms in force);
- carrying out the system calculations and the short circuitones (including the correct protection regulation);
- verifying the loading of the same type, as well as a of different type transformer units.
The short-circuit impedance measurement can beperformed by connecting the measurement installation to a low voltage (380/220V) source provided that highly accurate instrumentation enabling the automatic data processing is used.
Taken from a paper:
Power Transformer Units Condition Assessment Using VirtualInstrumentation
Discussion welcomed.
Advanced Online Moisture Measurements in Power transformers
Advanced Online Moisture Measurementsin Power Transformers
Maik Koch, Stefan Tenbohlen and Tobias Stirl*
University of Stuttgart, IEH, Pfaffenwaldring 47, 70569 Stuttgart, Germany* Areva Energietechnik GmbH, Activity Schorch Transformers, Rheinstrasse 73,41065 Mönchengladbach, Germany
Abstract – This paper investigates new approaches to determinewater in oil-paper-insulated power transformers.Moisture diffusion and equilibrium are described in termsof water potential. Measurement methods for water in oilpaper insulations were compared. Since the conventionalapplication of moisture equilibrium diagrams leads to erroneousresults, diagrams adapted to the moisture absorptioncapacity and ageing state of the involved materials werecreated. An advanced representation of equilibrium diagramsusing relative moisture in oil leads to much betterresults. Beyond this the moisture determination as activewater in oil and cellulose provides easy, accurate and continuousmeasurements and reflects directly the destructivepotential of water in oil paper insulations. Its integration inonline monitoring systems is shown.
SUMMARY:Main motivation for this investigation was to determinewater in oil-paper-insulated transformers accurateand continuously using equilibrium processes.- Moisture diffusion and equilibrium depends on thehighest possible entropy. This leads to the simple rule,that the relative moisture content CW,rel in adjacent materials becomes identical.
- The ability to dissolve water changes especially withageing of oil. Ageing products such as alcohols, aldehydes,ketones and acids are able to coalesce with waterand therefore increase water solubility.
- Ageing shifts the array of equilibrium curves towardsoil because of its intense increased water solubilitythereby that of cellulose decreases slightly.
- The old method to derive moisture in cellulose (in %)from moisture in oil (in ppm) via equilibrium diagramsis effected by substantial errors.
- Better results can be obtained, if moisture in oil relativeto saturation level (in %) is used instead of moisturein oil by weight (in ppm).
- Moisture relative to saturation or water activity is easy,continually and accurate measurable. Online monitoringsystems can derive moisture in paper from relativemoisture in oil using equilibrium diagrams adapted tothe moisture absorption capacity of paper.
- Active water or relative humidity directly reflects the destructive potential of water. It is therefore muchmore meaningful than the conventionally used waterrelated to weight. Thus water activity is a sufficient indicationfor water in oil paper insulations. Water activityin paper and pressboard is immediately derivable from relative moisture in oil.
To view the full paper
Discussion,Comment are welcomed.
Maik Koch, Stefan Tenbohlen and Tobias Stirl*
University of Stuttgart, IEH, Pfaffenwaldring 47, 70569 Stuttgart, Germany* Areva Energietechnik GmbH, Activity Schorch Transformers, Rheinstrasse 73,41065 Mönchengladbach, Germany
Abstract – This paper investigates new approaches to determinewater in oil-paper-insulated power transformers.Moisture diffusion and equilibrium are described in termsof water potential. Measurement methods for water in oilpaper insulations were compared. Since the conventionalapplication of moisture equilibrium diagrams leads to erroneousresults, diagrams adapted to the moisture absorptioncapacity and ageing state of the involved materials werecreated. An advanced representation of equilibrium diagramsusing relative moisture in oil leads to much betterresults. Beyond this the moisture determination as activewater in oil and cellulose provides easy, accurate and continuousmeasurements and reflects directly the destructivepotential of water in oil paper insulations. Its integration inonline monitoring systems is shown.
SUMMARY:Main motivation for this investigation was to determinewater in oil-paper-insulated transformers accurateand continuously using equilibrium processes.- Moisture diffusion and equilibrium depends on thehighest possible entropy. This leads to the simple rule,that the relative moisture content CW,rel in adjacent materials becomes identical.
- The ability to dissolve water changes especially withageing of oil. Ageing products such as alcohols, aldehydes,ketones and acids are able to coalesce with waterand therefore increase water solubility.
- Ageing shifts the array of equilibrium curves towardsoil because of its intense increased water solubilitythereby that of cellulose decreases slightly.
- The old method to derive moisture in cellulose (in %)from moisture in oil (in ppm) via equilibrium diagramsis effected by substantial errors.
- Better results can be obtained, if moisture in oil relativeto saturation level (in %) is used instead of moisturein oil by weight (in ppm).
- Moisture relative to saturation or water activity is easy,continually and accurate measurable. Online monitoringsystems can derive moisture in paper from relativemoisture in oil using equilibrium diagrams adapted tothe moisture absorption capacity of paper.
- Active water or relative humidity directly reflects the destructive potential of water. It is therefore muchmore meaningful than the conventionally used waterrelated to weight. Thus water activity is a sufficient indicationfor water in oil paper insulations. Water activityin paper and pressboard is immediately derivable from relative moisture in oil.
To view the full paper
Discussion,Comment are welcomed.
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