Advances in characterization and modelling of polymer ageing applied to electrical cables [15]

TeaM Cables Winter School – November 2021

Predictive and life modelling of cables through electrical NDT properties - Dr. Simone Vincenzo Suraci, University of Bologna, Italy

In this lecture, the modelling of the mechanical and electrical response, together with an aging modelling approach, is presented and discussed for low voltage cables used in a nuclear environment. After a brief reminder of the theory behind the presented models, a first focus is paid on a life predictive modelling of mechanical quantities, from which the dose corresponding to the cable failure, called dose-to-equivalent-damage (DED) values, has been obtained for each considered dose rate. However, the limitations given by the use of mechanical destructive measurements for cable aging assessment raised the interest into using different techniques e.g., electrical nondestructive tests (NDT). Therefore, a predictive modelling based on electrical quantities has been developed considering the monotone behaviour of tanδ at 100 kHz with aging. A limit value of tanδ corresponding to the different DEDs, namely tanδDED, has been obtained. It is found that tanδDED does not depend on the dose rate, but is only related to insulating material properties for the dose rate here analyzed.

Then, an aging model based on tanδ measurement is shown. This allows to evaluate the cumulative damage caused by changes of the dose rate due to abnormal and/or accidental conditions and estimate the residual life. The aging model is then applied to two case-studies. The aging level is calculated for a 20-year-old cable under service conditions. Then, two different accidental scenarios with different dose rates but the same absorbed dose are discussed. It is found that a lower dose rate applied for a longer period can bring the cable to failure, while with opposite characteristics it can provide a dramatic reduction of residual life, even if the cable can still be kept in service. This aging modelling approach can be of great help in scheduling maintenance operations, in particular following an event which could be associated with the exposure of cable insulation to high dose rate of radiation.

TeaM Cables has received funding from the Euratom research and training programme 2014-2018 under grant agreement No 755183