09_article_scopy - F E A T U R E A R T I C L E Dielectric...

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6 IEEE Electrical Insulation Magazine F E A T U R E A R T I C L E In this article, the feasibility of using time and frequency domain dielectric spectroscopy techniques to monitor the condition of oil-impregnated paper (OIP) condenser bushings is discussed. 0883-7554/07/$25/©2009IEEE Introduction B ushings are essential elements of many power equipments, including circuit breakers, capacitors, reactors, etc. Both high- and low-voltage windings are insulated from the core and from each other, and leads are brought out through insulating bushings. The two basic bushing designs are non-graded and capacitance-graded. The former is the simplest and the oldest. Capacitance graded bushings are available in four technologies: Resin Bounded paper (RB), Oil-Impregnated Paper (OIP), Resin Impregnated Paper (RIP) and Epoxy Resin Impregnated Paper (ERIP). OIP bushing, developed in the 1920s, is one of the most common types [1]. About 80% of all bushings in use today are of the OIP type. Explosive failure often follows bushing deterioration/degrada- tion, frequently resulting in catastrophic and expensive failure of a transformer and heavy damage to adjacent equipment. Accurate monitoring of the condition of bushings in service is therefore of vital importance. At present, routine maintenance tests most often used for checking the condition of bushings involve visual inspection and power factor/capacitance tests at line frequency [2]. The need to test power system insulation non-destructively and reliably in the field has driven the development of diagnostic tools based on changes in the dielectric properties of the insulation [3]–[14]. In this article, the feasibility of using time- and frequency- domain dielectric spectroscopy measurements to monitor the fabrication of OIP condenser bushings is discussed. Such mea- surements have been made on a laboratory OIP bushing model. The manufacturing process consisted of three stages, namely fabrication, drying and impregnation. Short-circuit between some of the condenser layers has also been simulated. Dielectric Spectroscopy Techniques The fundamental theories behind dielectric measurements are well known [6], [11], [13]. Dielectric phenomena are discussed in Jonscher’s publications [5]. However, to facilitate interpreta- tion of the measurements presented in this paper, a short review Dielectric Spectroscopy Techniques as Quality Control Tool: A Feasibility Study Key Words: Oil-Impregnated Paper (OIP) condenser bushings, dielectric spectroscopy, time domain, frequency domain. A. Bouaïcha and I. Fofana Canada Research Chair, tier 2, Insulating Liquids and Mixed Dielectrics for Electrotechnology (ISOLIME), Université du Québec à Chicoutimi, Chicoutimi, Qc, Canada. M. Farzaneh International Research Centre on Atmospheric Icing and Power Network Engineering (CenGivre), Université du Québec à Chicoutimi, Chicoutimi, Qc, Canada.
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09_article_scopy - F E A T U R E A R T I C L E Dielectric...

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