Amit Kumar MEHTA, Ram Naresh SHARMA, Sushil CHAUHAN

Thermal aging of solid insulation under dual temperature variation

The power transformer is one of the most expensive pieces of equipment in a high-voltage AC power system. An adequate monitoring system for power transformers can help in reducing the failure rate and thereby enhance system reliability and economic efficiency. Long-term and accelerated aging is not possible in real transformers, so prorated models of real transformers are preferred. This paper presents a study aimed at the aging of different cellulose papers and pressboards impregnated with transformer oil subjected to accelerated thermal aging at an oil temperature of 120 ◦ C and winding temperature of 150 ◦ C for time intervals extending from 0 to 500 h. The study manifests a close relationship between the degree of polymerization and the tensile strength of paper and pressboard that could be used in predicting the condition of solid insulation at various elevated temperatures. The graphical representation of various solid insulation properties and their correlation analysis has also been carried out.

PDF

___

[1] IEEE. IEEE C 57.91-1999 (R2002). IEEE Guide for Loading Mineral Oil Immersed Transformers. New York, NY, USA: IEEE, 2002.
[2] IEC. IEC Standard TS 62332-1. Electrical Insulation System (EIS) Thermal Evaluation of Combined Liquid and Solid Components-Part 1. General requirements. First Edition; 2005-09. Geneva, Switzerland: IEC, 2005.
[3] IEEE. IEEE Standard C 57.100-2011. IEEE Standard Test Procedure for Thermal Evaluation of Liquid-Immersed Distribution and Power Transformers. New York, NY, USA: IEEE, 2011.
[4] Emsley AM, Xiao X, Heywood RJ, Ali M. Degradation of cellulose insulation in power transformers. Part 4: Effect of aging on the tensile strength of paper. In: IEE Proceedings on Science Measurement and Technology; 2000. New York, NY, USA: IEEE. pp. 285-290.
[5] Lundgaard L E, Hansen W, Linhjell D, Painter T. Aging of oil-impregnated paper in power transformers. IEEE T Power Deliver 2004; 19: 230-238.
[6] Kolseth P, de Ruvo A. The cell wall components of wood pulp fibers. In: Bristow JA, Kolseth P, editors. Paper: Structure and Properties. New York, NY, USA: Marcel Dekker, 1986. pp. 1-25.
[7] Rigdahl M, Westerlind B, Hollmark H. Analysis of cellulose networks by the finite element method. J Mater Sci 1984; 19: 3945-3952.
[8] Ivarsson B, Steenberg B. Paper as a visco-elastic body applicability of Eyxings and Halseys try to stress-strain diagram of paper. Svensk Popperstidn 1947; 50: 419-432.
[9] Dai J. Study on failure mechanisms of transformer cellulose insulation with consideration of ester oil application. PhD, University of Manchester, Manchester, UK, 2009.
[10] Origin 6. Software. Northampton, MA, USA: OriginLab, 1999.
[11] OriginPro 8. Software. Northampton, MA, USA: OriginLab, 2007.
[12] Emsley AM, Stevens GC. Review of chemical indicators of degradation of cellulose electrical paper insulation in oil filled transformers. In: IEE Proceedings On Science Measurement and Technology; 1994. New York, NY, USA: IEEE. pp. 324-334.
[13] Wicks R, Prevost T, Glenn B, Marek R, Gasser HP. Industry standard for liquid-filled transformer insulation system - New model test. Weidmann-ACTI. In: Fifth Annual Technical Conference; November 2006.
[14] Prevost T, Wicks R, Gasser HP, Glenn B, Marek R. Estimation of insulation life based on a dual-temperature aging model. Weidmann-ACTI. In: Fifth Annual Technical Conference; November 2006.