Lifetime prediction cables

Two different approaches for lifetime prediction are presented. The underlying lifetime limiting processes have been identified in two cases. Mathematical expressions of chemical/physical relevance were used for the lifetime predictions for PE hot-water pipes and cables insulated with plasticized PVC. Accelerated testing, extrapolation and validation of the extrapolation by assessment of the remaining lifetime of objects aged during service conditions for 25 years were successfully applied to cables insulated with chlorosulfonated polyethylene. Polyolefin pipes exposed to chlorinated water showed a very complex deterioration scenario and it was only possible to find a method suitable for predicting the time for the depletion of the stabilizer system. 

Polyethylene has become one of the most widely used materials for electrical insulation due to its excellent dielectric properties and low cost. Original estimates of its probable lifetime using Arrhenius type extrapolation led to lifetime predictions of the order of forty years or more and yet a substantial number of failures in transmission and distribution cables have been observed at times under ten years. For 1977 failures on HMW URD cable totalled 1697 a failure rate of 3,08 per 100 miles while XLP cables were 0.53 per 100 miles and increasing (5). This work was undertaken to find out the role played by the polymer molecule under separate thermal and electrical stress. 

Gillen KT, Bernstein R, Qough RL, Celina M. Lifetime predictions for semi-crystalline cable insulation materials 1. Mechanical properties and oxygen consumption measurements on EPR materials. Polym Degrad Stab 2006 91 2146-56. 

As mentioned previously, lifetimes of more than Uo years have been predicted for polyethylene used for electrical insulation where electrical, thermal, mechanical and environmental stresses exist. The fact that cables are failing in a much shorter time period than predicted seems to point to an acceleration in rate of degradation over that assumed. This is directly opposite the results for thermal degradation obtained in this work where the rate of thermal degradation was found to be much slower than that predicted from high temperature experiments. 

Weathering Resistance Prediction of service life, although one of the most important areas of testing, is probably the most uncertain. Cable jackets of synthetic rubber used in the Distant Early Warning (DEW) Line in Northern Canada in the 1950s were forecast to have a 20-year lifetime. Most are stiU in service. Similar synthetic rubber wire coverings were used at that time for automotive wire harness when... 

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