Life estimation of LDPE film under stepped-stress voltage application

Abstract

Recently authors have proposed damage equalization method with step-stress tests for quick estimation of life exponent of power equipment insulation. Traditional constant-stress accelerated ageing tests for insulation are disadvantageous since outliers in sample data will always be there and some samples may not fail even after a long time. Such long duration life estimation tests are a major bottleneck towards development of better insulation materials. Step-stress breakdown tests for life estimation provide better acceleration without changing the mode of ageing, leading to lesser testing times but at the same time increase the complexity of analysis. In this paper the authors demonstrate the use of damage equalization method with stepstress tests for estimating the life of low density polyethylene (LDPE) insulation films. Polymeric insulation was so chosen due to its increasing use as a dielectric in diverse applications. Experiments were conducted on thin LDPE films under different step-times. Each sample was stressed till breakdown under each step-stress regime. Thereafter, inverse power law model is used in combination with Miner’s cumulative damage theory for calculation of power law exponent n. The power law exponent or life index n was calculated using least squares fitting. The iterative methodology implemented in the paper does not depend on numerical solutions for parameter estimation.