Propylene Cable Insulation Extrusion Without Crosslinking Defects
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Solution Overview
Problem
The existing manufacturing processes for medium- and high-voltage power cables face challenges such as limited recyclability of crosslinked polyolefin materials, restricted production rates due to crosslinking requirements, potential scorch phenomena, and safety issues with the injection of dielectric liquids during extrusion, which affect the homogeneity and mechanical/electrical properties of the insulating layers.
Innovation Solution
A process using a grooved barrel and/or barrier screw extruder to introduce a composition of propylene homopolymer or copolymer with a dielectric liquid at ambient temperature, ensuring homogeneous mixing and extrusion without high-pressure dielectric liquid injection, thereby preventing structural defects and safety hazards while maintaining good electrical and mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If crosslinked polyolefin materials are used for the insulating layer, then satisfactory electrical and mechanical properties are obtained and the cable can function at temperatures greater than 70°C, but the materials cannot be recycled and the crosslinking process limits the production rate
Solution Approach 1:
The patent changes the fundamental parameter of the insulating material from crosslinked polyolefin to thermoplastic polyolefin, eliminating the need for crosslinking while maintaining satisfactory electrical and mechanical properties. This allows continuous extrusion at high speeds without the production rate limitations imposed by crosslinking tunnels, thereby resolving the contradiction between reliability and productivity.
2Reliability
If crosslinking is carried out during extrusion to obtain satisfactory crosslinking degree, then the insulating layer achieves required properties, but XLPE particles form in the extruder and migrate into the insulating layer creating defects
Solution Approach 1:
The patent extracts the crosslinking step from the extrusion process, using thermoplastic polyolefin that does not require crosslinking. This eliminates the scorch phenomenon where premature crosslinking creates XLPE particles that compromise layer homogeneity, while still achieving the required insulating properties through the thermoplastic material itself.
3Reliability
If dielectric liquid is injected during extrusion stages, then electrical performance qualities are improved, but irregularities in movement and plasticizing of the polypropylene matrix occur along the barrel
Solution Approach 1:
The patent incorporates the dielectric liquid into the polypropylene matrix before extrusion begins, creating a pre-mixed composition. This preliminary action ensures uniform distribution throughout the material, preventing the irregularities in movement and plasticizing that would occur if the liquid were injected during extrusion, while still achieving the desired electrical performance.
4Reliability
If high-pressure injection of dielectric liquid is used during extrusion, then the dielectric liquid is effectively incorporated, but safety problems and damage to the injection device occur
Solution Approach 1:
The patent mixes the dielectric liquid with the polypropylene matrix before extrusion in a safe, low-pressure environment. This preliminary mixing action effectively incorporates the dielectric liquid without requiring high-pressure injection during extrusion, thereby eliminating the safety hazards and potential device damage associated with high-pressure injection systems.
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
This process enables the production of electric cables with extruded thermoplastic layers that match the performance of crosslinked XLPE layers, offering improved production efficiency, safety, and homogeneity without the need for complex safety devices, and allows for the use of recyclable materials.
Implementation Method 1
a stage during which the composition resulting from stage i) is conveyed from the feed zone towards one or more intermediate zones of the screw, making possible the transportation of the composition towards the head of the extruder located at the outlet of the extruder and the gradual melting of the thermoplastic polymer
Implementation Method 2
a stage of application, at the head of the extruder, of the composition resulting from stage ii) around the elongated electrically conducting element
Data Source
AI summary
The invention relates to a process for the manufacture of an electric cable comprising an extruded thermoplastic layer obtained from a composition comprising at least one dielectric liquid and at least one thermoplastic polymer chosen from a propylene homopolymer and copolymer, and also to a cable obtained by said process.