Paul J. Caronia

A new generation of tree-retardant crosslinked polyethylene (TR-XLPE) insulation

Additive tree-retardant crosslinked polyethylene (TR-XLPE) has been utilized as medium-voltage power cable insulation for over 25 years, and has been recognized for excellent performance in retention of breakdown strength in both accelerated aging and field-service conditions. Now, an improved TR-XLPE insulation has been developed which will enhance the longevity and reliability of medium-voltage cables, and will offer the potential to deliver long-life performance in high-stress cable designs. The new technology builds upon the proven history of additive TR-XLPE, and incorporates careful selection and optimization of additional functional elements to provide a balance of performance in terms of resistance to water-treeing, long-term heat stability, crosslinking efficiency and scorch-retardancy. A comparative review of performance will be provided for the improved TR-XLPE technology against todays TR-XLPE, through evaluation of mechanical and electrical properties on both material samples and medium voltage cables. An update on long-term accelerated cable aging of the new insulation will also be provided.

A next generation advanced water tree-retardant crosslinked polyethylene insulation for long life power cables

Underground cables used in wet environments that are insulated with crosslinked polyethylene (XLPE) have experienced premature failures due to a phenomena known as water treeing being associated with the failures. Developments in polyethylene insulation technology minimized this water-treeing induced problem through the use of water tree retardant crosslinked polyethylene (TR-XLPE). Since the introduction of TR-XLPE in 1983, evolutionary and sometimes revolutionary improvements have been made by both the compound producer and cable manufacturer leading to enhanced cable performance and greater value to the power industry A next generation, advanced TR-XLPE insulation that represents a major step change improvement in wet electrical performance has been developed. The next generation, advanced TR-XLPE insulation has improved wet electrical performance as demonstrated in laboratory studies and highly accelerated wet cable aging studies with distribution class cables. Additionally, this advanced TR-XLPE insulation shows the potential for use in high voltage cables. Cables insulated with the next generation, advanced TR-XLPE material are expected to further improve the reliability of distribution cable systems and potentially transmission cable systems while also providing cable design engineers the capability to optimize cable designs.

Ethylene alkene elastomers for cable insulation applications

Filled insulation compounds have predominantly been based on ethylene propylene rubber. Ethylene propylene rubber is commonly accepted to encompass ethylene propylene copolymers and ethylene propylene diene terpolymers. Advances in polymer catalyst technology have enabled a broader diversity of ethylene based polymers suitable for cable applications. The ICEA specification for medium voltage cables also allows for filled insulation compounds based on ethylene alkene copolymers. Ethylene alkene copolymers contain the traditional ethylene backbone though they can have a longer alkyl side chain or branch. This class of ethylene alkene elastomers can have the same physical properties, flexibility and electrical performance as ethylene propylene rubber based insulations.

Impact of semiconductive shield quality on accelerated aging cable performance

Semiconductive shield quality is critical to the life expectancy of power cables in medium, high, and extra-high voltage classes. The material properties and cable performance under accelerated conditions were compared for different commercial semiconductive shield compounds. All of the semiconductive shield compositions were found to be crosslinkable, contain similar levels of carbon black to be conductive, meet volume resistivity and physical properties required by IEC specifications and considered suitable for MV cable applications. The cables made with compound containing more protrusions and total chemical impurities had a much shorter characteristic life, less retained breakdown strength even as low as 7.8 kV/mm, and would be expected to have much less reliability than the cable with high quality semiconductive shields. The combination of these critical performance factors clearly indicates that semiconductive shields of poor quality can drastically reduce the effectiveness of an insulation material to achieve an expected long lifetime cable.