Polyolefin Cable Insulation Water Tree Resistance
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Solution Overview
Problem
Current polymer compositions for electric power cables face challenges with water tree resistance and crosslinking properties, leading to reduced service life and increased costs due to electrical breakdowns, especially in humid environments, and existing solutions compromise between water tree resistance and processing characteristics.
Innovation Solution
A crosslinkable polymer composition comprising a polyolefin, a polar copolymer, and a glycerol ester compound, which differs in polar comonomer units and carbon-carbon double bonds content, enhancing crosslinking efficiency and water tree resistance while improving processing characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polyethylene homopolymer is used as insulating material, then good dielectric properties (high breakdown strength and low power factor) are achieved, but the material is prone to water-treeing in the presence of water
Solution Approach 1:
The patent uses a composite material system consisting of polyethylene homopolymer blended with ethylene-vinyl acetate copolymer. This combination allows the material to maintain the excellent dielectric properties of polyethylene while the EVA copolymer component provides resistance against water-treeing, thus resolving the contradiction between dielectric performance and water-tree resistance
Solution Approach 2:
The patent changes the compositional parameters by controlling the blend ratio of polyethylene homopolymer and EVA copolymer, and adjusting the vinyl acetate content in the copolymer. By optimizing these parameters, the material achieves both high dielectric strength and improved water-tree resistance simultaneously
2Productivity
If peroxide compounds are added for crosslinking, then crosslinking efficiency is improved, but premature decomposition during extrusion causes scorch and inhomogeneity
Solution Approach 1:
The patent introduces silane coupling agent as an intermediary substance that facilitates crosslinking through a two-stage process. The silane first reacts with moisture to form crosslinkable groups, then undergoes condensation to form the crosslinked network. This intermediary mechanism allows crosslinking to occur after extrusion without premature decomposition, maintaining both productivity and homogeneity
Solution Approach 2:
The patent applies preliminary action by incorporating the silane coupling agent during the extrusion process, but the actual crosslinking reaction is triggered subsequently by moisture or heat treatment. This separates the mixing stage from the crosslinking stage, preventing scorch during extrusion while ensuring complete crosslinking afterward
3Speed
If crosslinking is performed at elevated temperature, then high crosslinking speed and efficiency are achieved, but decomposition of free-radical forming agents causes scorch
Solution Approach 1:
The patent replaces the traditional peroxide-based free-radical crosslinking mechanism with a silane-based crosslinking mechanism. Instead of relying on thermal decomposition of peroxides to generate radicals, the silane coupling agent reacts with moisture to form crosslinkable silanol groups, which then condense to form crosslinks. This substitution eliminates the scorching problem while maintaining high crosslinking efficiency
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The composition achieves improved electric breakdown strength after wet ageing, increased crosslinking speed, and reduced scorch formation, extending the service life of power cables and maintaining productivity.
Implementation Method 1
The layers of the cable are based on different types of polymers. Nowadays, low density polyethylene, crosslinked by adding peroxide compounds
Implementation Method 2
Many solutions have been proposed for increasing the resistance of insulating materials to degradation by water-treeing
Data Source
AI summary
The present invention relates to a crosslinkable polymer composition, comprising (i) a polyolefin, (ii) a polar copolymer, and (iii) a glycerol ester compound.