Life estimation of electrothermally stressed epoxy nanocomposites

Accelerated electrothermal aging tests were conducted at a constant temperature of 60°C and at different stress levels of 6 kV/mm, 7 kV/mm and 8 kV/mm on unfilled epoxy and epoxy filled with 5 wt% of nano alumina. The leakage current through the samples were continuously monitored and the variation in tan δ values with aging duration was monitored to predict the impending failure and the time to failure of the samples. It is observed that the time to failure of epoxy alumina nanocomposite samples is significantly higher as compared to the unfilled epoxy. Data from the experiments has been analyzed graphically by plotting the Weibull probability and theoretically by the linear least square regression analysis. The characteristic life obtained from the least square regression analysis has been used to plot the inverse power law curve. From the inverse power law curve, the life of the epoxy insulation with and without nanofiller loading at a stress level of 3 kV/mm, i.e. within the midrange of the design stress level of rotating machine insulation, has been obtained by extrapolation. It is observed that the life of epoxy alumina nanocomposite of 5 wt% filler loading is nine times higher than that of the unfilled epoxy.

[1]  M. Casale,et al.  On multistress aging of epoxy resins: PD and temperature , 2001 .

[2]  Franz Wolf,et al.  New Trends in the Insulation Technology of Rotating High Voltage Machines , 1999 .

[3]  M.J. Thomas,et al.  Polymer composite/nanocomposite processing and its effect on the electrical properties , 2006, 2006 IEEE Conference on Electrical Insulation and Dielectric Phenomena.

[4]  M. J. Thomas,et al.  AC breakdown characteristics of epoxy nanocomposites , 2011, IEEE Transactions on Dielectrics and Electrical Insulation.

[5]  T. S. Ramu,et al.  On the Estimation of Life of Power Apparatus Insulation Under Combined Electrical and Thermal Stress , 1985, IEEE Transactions on Electrical Insulation.

[6]  Y. Ohki,et al.  Proposal of a multi-core model for polymer nanocomposite dielectrics , 2005, IEEE Transactions on Dielectrics and Electrical Insulation.

[7]  M. J. Thomas,et al.  Partial discharge resistant characteristics of epoxy nanocomposites , 2011, IEEE Transactions on Dielectrics and Electrical Insulation.

[8]  J. R. Laghari,et al.  Accelerated life studies of polyimide film under electrical and thermal multistress , 1992, Conference Record of the 1992 IEEE International Symposium on Electrical Insulation.

[9]  F. Pohlmann,et al.  NANOTECHNOLOGY IN HIGH VOLTAGE INSULATION SYSTEMS FOR TURBINE GENERATORS – FIRST RESULTS , 2011 .

[10]  Y. Ohki,et al.  The role of nano and micro particles on partial discharge and breakdown strength in epoxy composites , 2011, IEEE Transactions on Dielectrics and Electrical Insulation.

[11]  J. Unsworth,et al.  The effect of electrical ageing on a cast epoxy insulation , 1993, Proceedings of Electrical/Electronics Insulation Conference.

[12]  S. Singha,et al.  Dielectric properties of epoxy nanocomposites , 2008, IEEE Transactions on Dielectrics and Electrical Insulation.

[13]  J. Samuel,et al.  EPOXY ALUMINA NANO-DIELECTRICS: A PROMISING MATERIAL FOR HIGH VOLTAGE INSULATION? , 2011 .

[14]  G.C. Stone,et al.  Electrical insulation for rotating machines-design, evaluation, aging, testing, and repair - Book Review , 2004, IEEE Electrical Insulation Magazine.

[15]  Qikai Zhuang,et al.  Life prediction for epoxy resin insulated transformer windings through accelerated aging tests , 2010, 2010 10th IEEE International Conference on Solid Dielectrics.

[16]  M. B. Srinivas,et al.  Experimental and statistical considerations in ageing studies on electrical insulation , 1994, Proceedings of 1994 4th International Conference on Properties and Applications of Dielectric Materials (ICPADM).

[17]  G. C. Stone.  The statistics of aging models and practical reality , 1993 .

[18]  G. Montanari,et al.  Polymer nanocomposites as dielectrics and electrical insulation-perspectives for processing technologies, material characterization and future applications , 2004, IEEE Transactions on Dielectrics and Electrical Insulation.

[19]  M. Di Lorenzo del Casale,et al.  A life model for epoxy resins subjected to PD activity at different temperatures , 2000, 2000 Annual Report Conference on Electrical Insulation and Dielectric Phenomena (Cat. No.00CH37132).

[20]  L. Schadler,et al.  A review on the importance of nanocomposite processing to enhance electrical insulation , 2011, IEEE Transactions on Dielectrics and Electrical Insulation.

[21]  M. Hikita,et al.  Effects of addition of nano-scale alumina and silica fillers on thermal conductivity and dielectric strength of epoxy / alumina microcomposites , 2010, 2010 10th IEEE International Conference on Solid Dielectrics.