Influence of the concentration of chemical elements in the age estimation of polymeric insulation

Abstract

The study of the lifetime performance of polymeric insulator is often based on incomplete data. Researchers face challenges of not having long observation time to gather complete lifetime data in order to make prediction with certainty. In this paper, we are proposing to use the best fitting polynomial interpolation approach to determine the lifetime model and extrapolate information towards the age of polymeric insulators. To gather the information such as the change of concentration of chemical element of polymeric insulation due to multiple stress conditions, high temperature vulcanized (HTV) silicone rubber specimens were subjected to accelerated degradation using an Accelerated Weathering Tester (QUV). Each specimen was subjected to accelerated aging cycle in accordance to ASTM G154 cycle 4 for a total of 3000 hours. The aging cycle goes through a cycle of 70 °C and ultraviolet exposure at irradiation intensity of 1.55 W/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> for eight hours followed by four hour condensation at 50 °C. Chemical element concentrations such as Carbon, Oxygen, Silicon and Aluminum were obtained and evaluated using a Scanning Electron Microscope (SEM) with energy dispersive x-ray (EDX). The concentrations of chemical elements are analyzed using polynomial interpolation method of multiple orders. First order to fifth order polynomial interpolation methods are investigated to determine the best fitting curve without significance divergence from the actual value or true value. The interpolation curve is used to estimate the age of an unknown aged sample. This investigation has revealed a novel method for determining a model that could describe the lifetime of polymeric insulators and extrapolation method for estimating the age for polymer insulator.