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.
