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Hd2512951299
Hd2512951299
Hd2512951299
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Hd2512951299

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  • 1. R.A. Venkata Lakshmi, T.S.R. Murthy / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.1295-1299 Studies on effect of Copper corrosion passivators on the Paper insulated copper conductor by XRD, SEM and EDX analysis R.A. Venkata Lakshmi*, T.S.R. Murthy** * (Chemist, Environment Division, AP GENCO, Vidyut Soudha, Hyderabad- 500 082, Andhra Pradesh, India) ** (Professor, Narsimha Reddy Engineering College, Hyderabad, Andhra Pradesh,)ABSTRACT The paper focuses on corrosion Different organo-sulphur compounds which arephenomena involving copper, corrosive sulphur very corrosive are present in new transformer oils,and solid insulation of oil-immersed depending on the crude oil origin and degree andtransformers. A study of the available type of refining. Some sulphur compounds have anmitigation technique such as passivation to affinity to metals and they act as copperreduce the effects of corrosion phenomena is passivators. Elemental sulfur is the most corrosivecarried out with the commercially available against copper, followed by hydrogen sulfide,passivator, Irgamet 39 (Toluiltriazole mercaptans, sulfides and disulfides. Sulfur organicdialkylamine) (ciba), with concentration of 100 compounds, where the sulfur atom is trapped in anppm. The paper insulated copper conductors aromatic structure (e.g. thiophenes and relatedwith transformer oil are aged for 1400 hrs at compounds), are usually considered as non140° C with and without passivators and tested reactive. Dibenzyldisulphide (DBDS), identified asboth paper insulation and copper samples with a major sulfur compound in several insulatingthe X-ray Diffraction (XRD), Scanning Electron mineral oils, seems to play a predominant role inMicroscope(SEM) and Energy dispersive X-ray the problem of corrosion phenomena. At highSpectroscopy (EDX). The SEM scan after ageing temperatures, DBDS reacts with copper conductorwith passivator shows the formation of thin film to form copper sulphides and impacts itsof passivator on the copper surface. The SEM, conductivity. Detachment of the copper sulfideXRD and EDX scans after ageing without layer formed on the naked copper surfaces causespassivator show the formation of copper the formation of suspended conductive particles,sulphide on the copper surface as well as on the which can act as nuclei for electrical dischargepaper insulation. between leads and the grounded tank. The copper sulfide growth on wrapped conductorsKey words: Copper corrosion, Dibenzyl is accompanied by its migration within the layersDisulphide, EDX, Mercaptans, Passivators, of insulating paper [1,2,3]. Formation ofSEM, XRD. conductive spots in the paper may cause the adjacent cellulose incapable to dissipate the heat 1. INTRODUCTION generated locally by the increase of conductivity of A Power transformer is composed of the insulation. This heat can result in a punctureseveral materials i.e. copper, iron, cellulose, wood, destroying the paper structure and allowing therubber, glues, polymers, and mineral oil which discharge between vicinal turns.undergo chemical reactions during operation at 1.1 Copper sulphide formation [4]high temperatures, overloading etc leading to Dibenzyl sulphide (DBS) and bisbenzyl (BiBZ)corrosion. Corrosion may cause the formation of will be formed in insulating oil as by-products ofcontaminants, both dissolved in the oil and forming copper sulfide formation between copper anddeposits on the paper or insoluble compounds that DBDS. The rate of sulphide formation reactionsprecipitate as sludge. Sulphur compounds cause seems to approximately double for every 10 º Ccorrosion, accelerate the asphalts production and increase of temperature. Temperature is not theworsen the dielectric properties of oil. The major only factor for copper sulphide formation. On-loadcorrosion process which leads to catastrophic tap changers (OLTC) switching operationsfailure of the transformers is the formation of involving high stresses (arcing) through the oil leadcopper sulphide that grows on the conductor to extensive copper sulfide formation.surface and on solid insulation. 1295 | P a g e
  • 2. R.A. Venkata Lakshmi, T.S.R. Murthy / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.1295-1299The mechanism of conversion of DBDS in the presence of copper and heat into copper sulphide is shown inFig.(1). S S dibenzyldisulphide + Cu CH3 S SH + + + + + Cu2S Dibenzylsulphide Stilbene Dibenzyl Benzyl mercaptan Toluene Copersulphide Figure 1. Mechanism of breakdown of DBDS 1.2 Copper passivator [5,6,7]Addition of copper passivator is one of the mitigation techniques that has been used to the largest extent. Anoptimum concentration of 100 ppm of passivator is added to inhibit the reaction of copper with corrosive sulfur.The passivators mostly used are BTA and derivatives such as toluiltriazole-dialkyl-amine commerciallyavailable as Ciba Irgamet39. The triazolic part of the molecule is likely oriented towards the conductor’ssurface, shielding it against the chemical attack of corrosive sulfur compounds and acting only as a potentiallyprotective agent. Irgamet 39, a triazole derivative is a liquid with density 0.95g/cm3 at 20° C, flash point isgreater than 150° C and offers low volatility, easy to handle, has excellent solubility in mineral oil and does notaffect the dielectric properties of transformer oils. It is a better passivator than BTA due to its good miscibilitywith oil. BTA is a granular solid at room temperature and requires heating and mixing to dissolve in the oil.Passivator structures are shown in Fig.(2) H3C N N N N H3C N CH3 H3C N N H H3C Benzo Triazole(BTA) Toluiltriazole-dialkylamine (Irgamet 39) Figure 2 The structure of BTA and Irgamet 39 passivators I. EXPERIMENTAL The XRD equipment used for this study is of The copper conductors of 8 inches length Philips make. It investigates crystalline materialcovered with a number of layers of cellulose paper structure, including atomic arrangement, crystallitewere dried at 105°C for 24 hours. The dried samples size and imperfections. It reveals information aboutwere impregnated with fresh dried filtered the crystal structure, chemical composition andtransformer oil with vacuum more than 1 torr at physical properties of materials and thin films.100° C and then immersed in fresh transformer oil. 2.1.1 PrincipleThe oil was found to contain trace amounts of It is based on observing the scattered intensity ofDBDS and Mercaptan Sulphur. The paper insulated an X-ray beam hitting a material as a function ofcopper conductors with and without passivators incident and scattered angle, polarization andwere aged in transformer oil for 1400hrs at 140° C wavelength or energy.in an oven. The metal passivator used in this 2.2. Scanning Electron Microscope(SEM)experiment is Irgamet39 as it is a liquid and easily The SEM used for this study is of Carl Zeissmiscible with oil. After ageing, the copper and the Germany make. It is used for high magnificationpaper samples were tested by XRD, SEM and EDX imaging of materials in determination of fibreanalysers. structure in wood and paper, metal fracture 2.1. X-ray Difractometer(XRD) surfaces, production defects. The surface coatings can be analysed by SEM and it is non-destructive. SEM in combination with EDX (Energy Dispersive 1296 | P a g e
  • 3. R.A. Venkata Lakshmi, T.S.R. Murthy / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.1295-1299X-ray Spectroscopy determines elemental Incident beam excites an electron in an inner shell,composition of samples. ejecting it from the shell while creating an electron 2.2.1 Principle hole where the electron was. An electron from anIt uses a focused beam of high-energy electrons to outer higher energy shell then fills the hole, and thegenerate a variety of signals like secondary difference in energy between the higher energyelectrons, back scattered electrons, diffracted back shell and the lower energy shell may be released inscattered electrons, photons, visible light and heat the form of an X-ray measured by EDX. Theat the surface of solid. The signals that derive from energy of the X-rays is characteristic of theelectron material interactions reveal information difference in energy between the two shells, and ofabout the external morphology (texture), chemical the atomic structure of the element from whichcomposition, crystalline structure and orientation of they were emitted. This allows the elementalmaterials. composition of the specimen to be measured. The 2.3.Energy dispersive X-ray Spectroscopy detector converts X-ray energy into voltage signals, It is used for elemental analysis or chemical which are sent to pulse processor, which measurescharacterization of material. signals and passes them onto an analyzer for data 2.3.1 Principle display and analysis. II. RESULTS AND DISCUSSIONS 3.1.The X-ray Diffraction studiesFigure 3. Figure 4.XRD scan of copper sample of paper insulated copper XRD scan of Paper Sample on copper conductorconductor after ageing in oil without passivator at after ageing in oil without passivator at 140 °C140°C for 1400 hr for1400 hr Figure 5. XRD scan of Paper Sample on copper conductor after ageing in oil with passivator at 140 °C for 1400 hrThe presence of copper sulphide on copper paper sample on copper conductor aged inconductor could not be established using XRD due transformer oil for 1400 hrs at 140 °C withoutto poor resolution and it indicates characteristic passivator. The scan indicates Cu2S peaks at thetabands due to copper only. In addition to copper, the (ø) values of 32, 48, 58, 62 on paper insulationXRD spectrum shows presence of calcium also aged with transformer oil. Fig. (5) shows XRDwhich could have come from the cellulose paper as scan of Paper Sample on copper conductor aftershown in Fig. (3). Fig. (4) shows the XRD scan of ageing in oil with passivator at 140 °C for 1400 hr. 1297 | P a g e
  • 4. R.A. Venkata Lakshmi, T.S.R. Murthy / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.1295-12993.2. Scanning Electron Microscope (SEM) studiesFigure 6 Figure 7SEM scan of copper sample of paper insulated copper SEM scan of copper sample of paper insulated copperconductor after ageing in oil without passivator at 140 conductor after ageing in oil with passivator at 140°C for1400 hr °C for 1400hr Figure 8 SEM scan of paper sample on copper conductor after ageing in oil with out passivator at 140 °C for 1400 hrFig. (6) shows SEM analysis of copper sample of paper insulated copper conductor after ageing withtransformer oil without passivator at 140° C for 1400 hr. This indicates globules of copper sulphide on agedcopper surface. Fig. (7) shows SEM analysis of copper sample of paper insulated copper conductor after ageingwith transformer oil with passivator at 140° C for 1400 hr. This indicates formation of a uniform film of thepassivator on the conductor surface. Fig. (8) shows SEM analysis of paper sample after ageing in transformer oilwithout passivator at 140° C for 1400 hrs. This picture clearly shows contamination on the paper insulation inwhich all the fiber surfaces and the gaps between the fibers encrusted with the copper sulfides. The coppersulfide formed can be visibly seen on the paper insulation in some cases and ranges considerably in colorationdepending upon severity, closeness to the conductor and other factors. The copper sulfide deposit is scattered onthe paper insulation. 3.3 Energy dispersive X-ray analysis (EDX) studiesFigure 9 Figure 10EDX scan of copper sample of paper insulated copper EDX scan of copper sample of paper insulated copperconductor after ageing in oil with out passivator at 140 conductor after ageing in oil with passivator at 140°C°C for1400 hr for 1400 hr 1298 | P a g e
  • 5. R.A. Venkata Lakshmi, T.S.R. Murthy / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.1295-1299 Figure 11 EDX scan of paper sample on copper conductor after ageing in oil with out passivator at 140 °C for1400 hrFig. (9) shows EDX scan of copper sample of REFERENCESpaper insulated copper conductor after ageing in oil [1] Lewand Lance R (2002), The Role ofwithout passivator at 140° C for 1400 hr. This Corrosive Sulfur in Transformers andindicates copper and sulphur peaks on aged copper Transformer Oil, Proceedings of the Sixty-surface. The sulphur peak is seen at 2.1 keV and Ninth Annual International Conference ofcopper at 7.9 and 8.4 keV. Fig. (10) shows EDX Doble Clients, Boston, MA, Insulatingscan of copper sample of paper insulated copper Materials Session.conductor after ageing in transformer oil with [2] Wilson, A.C.M (1980), Insulating Liquids:passivator at 140° C for 1400 hr. The minute Their Uses, Manufacture and Propertie,sulphur peak is seen at 2.1 keV and copper peaks at IEEE, (New York and UK).7.9 and 8.4 keV, but the intensity of the sulphur [3] Vander Tumiatti, Michela Tumiatti,peaks is drastically reduced due to formation of Riccardo Maina, Carlo Roggero,thin film of passivator on the copper surface. Fig. Integrated methods for the determinations(11) shows EDX scan of paper sample on copper of corrosivity, aging, finger printing asconductor after ageing with transformer oil without well as the diagnosis, decontamination,passivator at 140° C for 1400 hr. This also shows depolarization and detoxification ofthe deposition of copper sulphide. mineral insulating oils & transformers, Sea Marconi Technologies Sas, Italy.III. CONCLUSION [4] Vander Tumiatti, R. Maina, F. Scatiggio, Copper sulphide formation is one of the M. Pompili and R. Bartnikas (2006),possible corrosion mechanisms involving the Corrosive Sulfur in mineral oils: itscorrosive sulphur and paper insulated copper detection and correlated powerconductor. transformer failures”, Proc. IEEE Int.The SEM scan after ageing the paper insulated Symposium on Electrical Insulation,copper conductor in transformer oil with passivator Toronto, June 12-14at 140° C for 1400 hr shows the formation of thin [5] Amimoto,T, Nagao,E.: Tanimura, J.;film of passivator on the copper surface. The SEM, Toyama,S.; Yamada,N. Duration andXRD and EDX scans after ageing the paper mechanism for suppressive effect ofinsulated copper conductor in transformer oil triazole-based passivators on copper-without passivator at 140° C for 1400 hr indicate sulfide deposition on insulating paperscattered deposit of copper sulphide showing the Mitsubishi Electr. Corp., Ako Dielectricsformation of copper sulphide on the copper surface and Electrical Insulation, IEEEas well as on the paper insulation. transactions on Volume: 16, Issue: 1, Page(s)-257-264.IV. ACKNOWLEDGEMENT [6] Prof. Bruce Pahlavanpour and Mr. Kjell The authors are thankful to the R & D Sundkvist, Mineral Insulating OilLaboratories of AP TRANSCO and AP GENCO Passivation Effectiveness of Passivation tofor continuous support and valued guidance. stop Copper Deposition Nynas Naphthenics Ltd, Wallis House, 76 North street, Guildford Survey, GUI 4AW, UK. [7] Katritzky, A.R.; Lan, X.; Yang, J. Z.; Denisko, O.V, Properties and Synthetic Utility of N-Substituted Benzotriazoles. Chem. Rev., (1998), 409-548. 1299 | P a g e

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