Overhead Conductor with stranded Multiwire Composite Core in Aluminium Sheath – IEC TS 62818 Arrhenius testing of Resins

(PMC) conductors, specifically those with carbon fibre and epoxy composite cores, which offer a significantly higher strength-to-weight ratio and minimal thermal expansion compared to traditional steel-reinforced conductors. The adoption of these advanced composite materials is gaining momentum in the transmission industry, particularly following the issuance and unanimous approval of the IEC Technical Specification TS62818-1 Ed1, which formalizes testing and performance criteria for polymeric matrix composite cores in overhead lines.

The primary objective of the study is to compare the thermal ageing performance of two epoxy resin systems, referred to as Type A and Type B, used as the matrix in carbon fibre composite multi-wire cores. The motivation for this comparison arises from both performance requirements set by system operators and manufacturers, as well as the need to mitigate supply chain risks by diversifying resin choices. The work aims to provide data-driven insights into the behavior of these materials under prolonged thermal stress, supporting industry efforts to select suitable materials for high-temperature, low-sag (HTLS) overhead line applications.

The core methodology involves accelerated thermal ageing tests based on the Arrhenius theory, as detailed in the IEC TS62818-1 standard. Samples, consisting of multi-wire composite cores encased in aluminum tubes, are prepared, sealed, and subjected to elevated temperatures for extended periods (using at least three distinct temperature levels). Tensile strength and modulus, as well as glass transition temperature (Tg), are measured before ageing using standardized testing protocols (ISO 527-5:2021 for tensile properties and ISO 6721-5 for T g).

The end-point criterion for ageing is set as a ≤5% or ≤10% reduction in tensile strength relative to initial values, simulating a typical 40- to 50-year service life.

Results show that Type B resin composite cores deliver slightly higher initial tensile strength and modulus than Type A, despite a marginally lower initial Tg. During the Arrhenius thermal ageing tests, Type B resin exhibits superior durability at elevated temperatures, with delayed onset and slower progression of strength degradation compared to Type A. Arrhenius plot analysis further reveals that the time-to-failure for Type B resin is more consistent across temperatures, resulting in a higher extrapolated maximum continuous service temperature

(160.3 °C for Type B vs 148.8 °C for Type A for a required 40-year lifetime). This improved performance is attributed to greater thermal stability and more uniform degradation characteristics of the Type B resin system.

In conclusion, the study demonstrates that Type B epoxy resin systems used in carbon fibre composite conductors offer enhanced long-term thermal performance and reliability. These findings have substantial implications for the design and selection of conductor materials in overhead transmission lines, supporting safer and more efficient operation under increasingly demanding thermal conditions. The research also highlights that initial Tg alone is not a sufficient indicator of long-term durability under thermal ageing, reinforcing the value of comprehensive accelerated ageing protocols for material qualification.