AP08_4.vp 1 Indroduction Insulating oils should have stable high-quality properties, not only in the original state, but also during the up time in operation. The stability of insulating oils has an elementary meaning during operation, because they work under high temperatures usually in the presence of oxygen, so they should be oxidation resistant. The oxidation of oil increases its acidity and the content of sediments Low sediment values indicate high oxidation stability, leading to long oil life. Minimizing the creation of sediments, the dielectric dissipation factor, corrosion of met- als, electric failures maximizes the insulating ability of oil. Oxidation stability is measured by IEC 61125, method C [2, 3], or by the ČEZ – ORGREZ method [1]. Oxidation stability is an indicator that allows us to set stricter limits for oils in special applications. In some coun- tries, striker limits or other requirements and tests are imposed. 2 ČEZ – ORGREZ methodology During the test, the sample of new or reclaimed oil is exposed to conditions simulating a load application, similar to the load during operation. Individual factors are sim- plified. High-quality parameters are periodically monitored until sediments form and the oil is no longer usable. 2.1 Laboratory instruments, devices and chemicals [1] � glass sulphonation flask, 6000 ml � separation trap 250 ml � tube immune temperatures and oils (teflon, silicon) � air compressor � laboratory drying chamber with temperature regulation (100 °C) � plastic component syringe for taking samples (150 ml) � clean copper wire without surface treatment (unvarnished) � analytical scales, precision 0.001 g � measuring cylinder, 2000 ml. 2.2 Preparation of the experiment, and testing process [1] Before the test begins, the initial high-quality parameters are determined and 500ml is taken away from the oil sample. A measuring cylinder is used to measure out 5000 ml of oil, marked out for testing, into the sulphonation flask. The required quantity of copper wire will be added to the oil – 10g (quantity cca. 0.1 cm2/g of oil) to each litre of oil. The flask with oil will be put into the laboratory drying chamber, at a temperature of 100 °C. Using tubes perhaps made of glass air will be conducted into the samples to ensure delivery of condensed fluid into the separation trap outside the drying chamber. A control test and verification of the temperature regu- lated in the drying chamber will be carried out every day. Some, of the samples, will be removed at weekly intervals to determine the values of selected parameters (acidity, in- terfacial tension and content of inhibitors – 1× per week, dielectric dissipation factor – 1× per 3 weeks). The test will be completed when sediments insoluble in n-heptane are present or whenthere are no more samples for continuing the test or after 840 hours of testing. 2.3 Comparison with the ČSN EN 61125 standard, method C This method describes a test for interpreting the oxida- tion stability of new hydrocarbon insulating fluids under accelerated conditions, without reference to whether antioxi- dant additives are present. Test conditions: The filtered fluid sample oxidizes under the following conditions [3]: � oil weight: 25 g � 0.1 g, � oxidation gas: air, � gas flow speed: 0.15 l/h � 0.015 l/h, � test period: � 164 h – for uninhibited oil, � 500 h – for inhibited oil, � accelerator: copper wires in quantities 28.6 cm2 � 0.3 cm2 measured oil. 30 © Czech Technical University Publishing House http://ctn.cvut.cz/ap/ Acta Polytechnica Vol. 48 No. 4/2008 Thermal – Oxidation Stability of Insulating Fluids P. Semančík, R. Cimbala, K. Záliš This paper deals with the thermal – oxidation stability of insulating fluids by the ČEZ– ORGREZ test method [1]. It describes the principle test method as a preparation of experiment and the thermal – oxidation stability measuring of insulating oil. Keywords: oxidation stability, oil life, dielectric dissipation factor, ČEZ – ORGREZ test method. 3 Experimental results The thermal – oxidation stability test of insulating oil was made using the ČEZ – ORGREZ method [1]. Power transformer insulating oil was used as a sample. Further infor- mation about the sample confidental to the manufacturer and to the plant operator. During the experiment, the data, interpreted in (Table 1) was measured [4]. The principle of the test is based on the air oxidation of the measured oil with added accelerator at a given temperature. The test was carried out under the following conditions [1]: � temperature 100 °C, � volume of oil samples 5 l, � bubbling of oil dried and refined by air in larger amounts than are needed for reaction of oil with the air, � accelerator: copper wires in quantities cca 0.1 cm2/g mea- sured oil. The separation trap, placed outside the drying chamber, gathers the condensed fluid released during the test. The values measured in dependency on the length of test periods are recorded in tables (Table 1), which show the deg- radation process of the oil until the moment when sediments insoluble in n-heptane form, or until the test is terminated. The graphic dependencies in Figs. 1–4 were made from the measured values monitoring the individual parameters. Monitored parameters [2–5]: tg� – dielectric dissipation factor, �r – dielectric permittivity, � – volume resistivity, ČK – determination of acidity, � – determination of interfacial tension of oil against water, Qi – contents of inhibitors. © Czech Technical University Publishing House http://ctn.cvut.cz/ap/ 31 Acta Polytechnica Vol. 48 No. 4/2008 Test period (h) tg� (×10�2) �r (-) � (G� m) ČK � Qi Sediments insoluble in the n-heptan 20 °C 70 °C 90 °C 20 °C 70 °C 90 °C 20 °C 70 °C 90 °C 0 0.018 0.075 0.138 2.257 2.199 2.175 2203.8 598.1 232.9 0.004 51 0.35 - 168 0.006 50 0.37 - 336 0.040 0.126 0.385 2.255 2.159 2.136 856.8 178.5 107.1 0.006 49 0.38 - 504 0.007 49 0.37 - 672 0.010 47 0.29 - 840 0.076 0.832 1.473 2.263 2.207 2.182 561.4 147.3 122.8 0.012 47 0.29 - 1008 0.011 45 0.27 - 1176 0.016 44 0.27 - 1344 0.122 0.886 1.866 2.262 2.190 2.165 235.8 108.8 48.3 0.016 43 0.25 - 1512 0.016 42 0.24 - 1680 0.021 41 0.23 - 1848 0.200 2.509 3.761 2.268 2.191 2.164 169.3 52.0 24.7 0.026 41 0.23 - 2016 0.030 39 0.23 - 2184 0.037 38 0.22 - 2352 0.168 3.300 5.978 2.271 2.202 2.181 127.4 15.2 9.5 0.048 37 0.16 - 2520 0.065 37 0.13 - 2688 0.079 35 0.08 - 2856 0.483 7.890 17.648 2.300 2.244 2.227 51.2 2.7 1.0 0.132 28 0.00 presence ČK – mg KOH/g, � – mN/m Qi – %hmot., F – sample filtered using white tape filter paper (6 – 6.8 �m) before the measurement. Table 1: Values measured by the ČEZ – ORGREZ test method [4] 4 Conclusion The oxidation stability of oil is evaluated by period of time until sediments for that are soluble in the insulating oil (in- soluble in the n-heptane), or by the creation of sediments that are insoluble in insulating oil. In the test of thermal-oxidation stability the submitted sample of insulating oil degraded in 2856 hours. This was documented by the presence of sediments insoluble in the n-heptanes. The thermal – oxidation stability test was cerried out using, the ČEZ – ORGREZ method. The graphic depend- encies were assessed from the monitored oil parameters. Acknowledgments This work was supported by scientific Grant Agency of the ministry of Education of the Slovak Republic and the Slovak Academy of Sciences under project VEGA No. 1/3142/06 and APVV-20-006005. References [1] SOP 2-32/72: Tepelně – oxidační stabilita izolačných kapalin podle metodiky ORGREZ a.s..ORGREZ a.s., Brno, Czech Republic, 2004. [2] STN EN 60296: Kvapaliny na elektrotechnické aplikácie. Nepoužité minerálne izolačné oleje pre transformátory a spína- če. Slovenský ústav technickej normalizácie, Bratislava, 2005. [3] ČSN EN 61125: Nové izolační kapaliny na bázi uhlovodíků. Zkušební metody na vyhodnocování oxidační stálosti. Český normalizační institut, 1996. [4] ORGREZ, a.s.: Protokol o měření Zkouška tepelně-oxidační stálosti izolačního oleje – metodika ČEZ-ORGREZ. ORGREZ a.s. Divize elektrotechnických laboratoří, Praha, 2006. [5] ČEZ, a.s.: Profylaktika minerálních izolačních olejů. Pod- niková norma 00/08 rev0. 32 © Czech Technical University Publishing House http://ctn.cvut.cz/ap/ Acta Polytechnica Vol. 48 No. 4/2008 0 2 4 6 8 10 12 14 16 18 20 0 500 1000 1500 2000 2500 3000 t [h] tg�� �×10 �2 � 20°C 70°C 90°C Fig. 1: Dependence of tg� 2 12. 2 14. 2 16. 2 18. 2 20. 2 22. 2 24. 2 26. 2 28. 2 30. 2 32. 0 500 1000 1500 2000 2500 3000 � r [-] t [h] 20°C 70°C 90°C Fig. 2: Dependence of �r 0 500 1000 1500 2000 2500 0 500 1000 1500 2000 2500 3000 t [h] � [G� m] 20°C 70°C 90°C Fig. 3: Dependence of � [mN/m] 0 00. 0 05. 0 10. 0 15. 0 20. 0 25. 0 30. 0 35. 0.40 0 500 1000 1500 2000 2500 3000 t [h] ÈK [mg KOH/g] Qi [% hmot.] 0 10 20 30 40 50 60 CK Qi � Fig. 4: Dependence of ČK, Qi, � © Czech Technical University Publishing House http://ctn.cvut.cz/ap/ 33 Acta Polytechnica Vol. 48 No. 4/2008 Ing. Peter Semančík phone: +421 556 023 560 e-mail: peter.semancik@tuke.sk Doc. Ing. Roman Cimbala, Ph.D. phone: +421 556 023 557 e-mail: roman.cimbala@tuke.sk Department of Electric Power Engineering Technical University in Košice Faculty of Electrical Engineering and Informatics Mäsiarska 74 041 20 Košice, Slovak Republic Doc. Ing. Karel Záliš, CSc. phone: +420 224 352 369 e-mail: zalis@fel.cvut.cz Department of Electrical Power Engineering Czech Technical University in Prague Faculty of Electrical Engineering Technická 2 166 27 Prague 6, Czech Republic << /ASCII85EncodePages false /AllowTransparency false /AutoPositionEPSFiles true /AutoRotatePages /None /Binding /Left /CalGrayProfile (Dot Gain 20%) /CalRGBProfile (sRGB IEC61966-2.1) /CalCMYKProfile (U.S. Web Coated \050SWOP\051 v2) /sRGBProfile (sRGB IEC61966-2.1) /CannotEmbedFontPolicy /Error /CompatibilityLevel 1.4 /CompressObjects /Tags /CompressPages true /ConvertImagesToIndexed true /PassThroughJPEGImages true /CreateJobTicket false /DefaultRenderingIntent /Default /DetectBlends true /DetectCurves 0.0000 /ColorConversionStrategy /CMYK /DoThumbnails false /EmbedAllFonts true /EmbedOpenType false /ParseICCProfilesInComments true /EmbedJobOptions true /DSCReportingLevel 0 /EmitDSCWarnings false /EndPage -1 /ImageMemory 1048576 /LockDistillerParams false /MaxSubsetPct 100 /Optimize true /OPM 1 /ParseDSCComments true /ParseDSCCommentsForDocInfo true /PreserveCopyPage true /PreserveDICMYKValues true /PreserveEPSInfo true /PreserveFlatness true /PreserveHalftoneInfo false /PreserveOPIComments true /PreserveOverprintSettings true /StartPage 1 /SubsetFonts true /TransferFunctionInfo /Apply /UCRandBGInfo /Preserve /UsePrologue false /ColorSettingsFile () /AlwaysEmbed [ true ] /NeverEmbed [ true ] /AntiAliasColorImages false /CropColorImages true /ColorImageMinResolution 300 /ColorImageMinResolutionPolicy /OK /DownsampleColorImages true /ColorImageDownsampleType /Bicubic /ColorImageResolution 300 /ColorImageDepth -1 /ColorImageMinDownsampleDepth 1 /ColorImageDownsampleThreshold 1.50000 /EncodeColorImages true /ColorImageFilter /DCTEncode /AutoFilterColorImages true /ColorImageAutoFilterStrategy /JPEG /ColorACSImageDict << /QFactor 0.15 /HSamples [1 1 1 1] /VSamples [1 1 1 1] >> /ColorImageDict << /QFactor 0.15 /HSamples [1 1 1 1] /VSamples [1 1 1 1] >> /JPEG2000ColorACSImageDict << /TileWidth 256 /TileHeight 256 /Quality 30 >> /JPEG2000ColorImageDict << /TileWidth 256 /TileHeight 256 /Quality 30 >> /AntiAliasGrayImages false /CropGrayImages true /GrayImageMinResolution 300 /GrayImageMinResolutionPolicy /OK /DownsampleGrayImages true /GrayImageDownsampleType /Bicubic /GrayImageResolution 300 /GrayImageDepth -1 /GrayImageMinDownsampleDepth 2 /GrayImageDownsampleThreshold 1.50000 /EncodeGrayImages true /GrayImageFilter /DCTEncode /AutoFilterGrayImages true /GrayImageAutoFilterStrategy /JPEG /GrayACSImageDict << /QFactor 0.15 /HSamples [1 1 1 1] /VSamples [1 1 1 1] >> /GrayImageDict << /QFactor 0.15 /HSamples [1 1 1 1] /VSamples [1 1 1 1] >> /JPEG2000GrayACSImageDict << /TileWidth 256 /TileHeight 256 /Quality 30 >> /JPEG2000GrayImageDict << /TileWidth 256 /TileHeight 256 /Quality 30 >> /AntiAliasMonoImages false /CropMonoImages true /MonoImageMinResolution 1200 /MonoImageMinResolutionPolicy /OK /DownsampleMonoImages true /MonoImageDownsampleType /Bicubic /MonoImageResolution 1200 /MonoImageDepth -1 /MonoImageDownsampleThreshold 1.50000 /EncodeMonoImages true /MonoImageFilter /CCITTFaxEncode /MonoImageDict << /K -1 >> /AllowPSXObjects false /CheckCompliance [ /None ] /PDFX1aCheck false /PDFX3Check false /PDFXCompliantPDFOnly false /PDFXNoTrimBoxError true /PDFXTrimBoxToMediaBoxOffset [ 0.00000 0.00000 0.00000 0.00000 ] /PDFXSetBleedBoxToMediaBox true /PDFXBleedBoxToTrimBoxOffset [ 0.00000 0.00000 0.00000 0.00000 ] /PDFXOutputIntentProfile () /PDFXOutputConditionIdentifier () /PDFXOutputCondition () /PDFXRegistryName () /PDFXTrapped /False /CreateJDFFile false /Description << /ARA /BGR /CHS /CHT /CZE /DAN /DEU /ESP /ETI /FRA /GRE /HEB /HRV (Za stvaranje Adobe PDF dokumenata najpogodnijih za visokokvalitetni ispis prije tiskanja koristite ove postavke. 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