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Abstract
A new method to estimate the average dielectric constants of cable sections that have undergone aging is proposed. By comparing the experimental Joint Time-Frequency Domain Reflectometry waveform signatures from a new and an aged cable of the same type, it is demonstrated that the change in the average dielectric constant of the insulation material due to aging can be estimated. For example, for a cable containing Cross-Linked Polyethylene insulation, accelerated aging tests based on the modified Arrhenius equation that simulate 120 years of aging at 50 °C operating temperature show that the dielectric constant of the insulation decreases by more than 34.5%. The same tests performed on another cable containing Ethylene-Propylene Rubber insulation show that the average dielectric constant of the insulation decreases by 10.4%. The efficacy of the method is further demonstrated by estimating the increase in the average dielectric constant of a wedge section of a cable that contained water intrusion.
Acknowledgement
This work was supported in part by the US Office of Naval Research under Grant N00014-08-1-0080.