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Study on the Electrochemical Method for Determining Oxidation Stability of Transformer Oil Rapidly

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Tutor: HeDeLiang
School: Hunan University
Course: Chemical Engineering and Technology
Keywords: Transformer oil,Antioxidant,Acid value,Polypyrrole,Modified electrode,Naphthoqui
CLC: TM855
Type: Master's thesis
Year:  2013
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Abstract:
Transformer is the key equipment of power industry for maintaining the powersystem reliability. Its electrical operation is of great importance for power saving, aswell as for the stability of national economy. Transformer oil, a derivative ofpetroleum crude, is used for filling in transformers as major electro-insulation andcooling fluids. In recent years, several transformer faults occurred by the partialdischarge and lack of oil. With the development of ultra high voltage transformers,higher quality supervision of transformer oil is required. The oxidation stability is anindex that can reflect the operation healthy of transformer oil directly, therefore, itsevaluation plays an important role in oil diagnose. However current methods foroxidation stability determination were mainly served on the lubrication oil and turbineoil, not on transformer oil. A new rapid, well-controlled method should thus beestablished for the determination.£¨1£© In this paper, a new electrochemical method was developed for determi ningthe antioxidant in transformer oil. Glassy carbon electrode £¨5mm£©,0.1mol/L KOHethanol solution and differential pulse voltammetry were used as working electrode,supporting electrolyte and determining technology respectively. The standard curveequation of antioxidant in transformer oil was C=0.0261H-0.0074,[where Crepresented the mass concentration of T501£¨%£©, H represented the peak current £¨¦ÌA£©,R=0.9994]. This method was successfully applied in the real oil samples. Comparedwith the liquid chromatograph and ultraviolet spectrophotometry method, thiselectrochemical method was time-saving with low detection limit, high accuracy andgood repeatability. This research of electrochemical technology to detect the contentsof antioxidant in transformer oil has important value in theory and practice. In addition,less similar study and application in the field of domestic power demonstrats the str ongnovelty of this research.£¨2£© A polypyrrole-modified glassy carbon electrode £¨PPy/GC electrode£© wasprepared and the voltammetric behavior of naphthoquinone in the presence of acid atPPy/GC electrode was studied. A well-defined new reduction appeared at a morepositive potential and the new reduction peak current presented to be linearly related tothe acid value of oil, based on it, a new method for determining AV of transformer oilwas developed using PPy/GC electrode in linear sweep voltammetry. A standard curvewas obtained in the acid value range of0.01to0.40mgKOH/g for naphthenic acid, with a sensitivity of39.42¦ÌA0.5/£¨mgKOH/g£© and the detection limit of0.0014mgKOH/g £¨S/N=3, RSD=2.247%£©. Moreover, the proposed method has beensuccessfully applied for the acid value determination in several transformer oil sampleswith less time of100s per one oil sample. Simultaneously, sample color and turbiditycause no interference on the analytical results. This rapid and straightforward methodcan be easily applied to the on-site testing and environmental safe.£¨3£© A new improved potentiometric titration method was developed according tothe standard method £¨GB/T7304£©. By the improvement of titrant and solvent£¬ theapparent acidity of acidic component was enhanced, moreover, the dissoluvability ofheavy oil sample and the extraction ability to acid were increased. This method candetermine the end point of titration based on potential jump, which is suitable todetermine the acid value of various kinds of complex products.£¨4£© A new rapid method to determine the oxidation stability was developedaccording to the standard method £¨SH/T0206-92£©. The optimum aging condition was40mL/min oxygen flux,1.0g copper powder £¨catalyst£© and130¡À0.5¡æ£¨agingtemperature£©. The content of antioxidant and acid value of transformer oil weredetermined by the electrochemical method and improved potentiometric titrationmethod respectively. Meanwhile the working curve between the content of antioxidantand acid value in aged transformer oil was constructed. Using this new method, theacid value can be attained directly through the contents of antioxidant, moreover, theoxidation stability of oil can be determined rapidly by the comprehensive evaluation ofthese two index. This rapid detection method can meet the demands about the real-timeand on-site quality supervision of transformer oil in operation.
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