Silane Crosslinked Polyolefin Cable Insulation
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Solution Overview
Problem
High voltage direct current (HV DC) power cables face challenges with electrical conductivity, leading to heat generation and thermal runaway due to high conductivity of insulating materials, which is not adequately addressed by conventional crosslinking methods that require costly and time-consuming degassing steps, and are limited by production line constraints.
Innovation Solution
A crosslinked power cable with a polyolefin composition containing an antioxidant and peroxide in an amount less than 35 mmol -O-O-/kg, which reduces electrical conductivity to 45 fS/m or less, allowing for reduced heat formation and improved mechanical properties without the need for degassing, enabling efficient production and enhanced performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional crosslinking methods using peroxide are used, then mechanical strength and heat resistance are improved, but volatile decomposition products are generated requiring time-consuming and costly degassing steps
Solution Approach 1:
The patent changes the chemical parameter of the crosslinking agent from conventional peroxide to a peroxide-free system using silane-based crosslinking. This parameter change eliminates volatile decomposition products while maintaining crosslinking effectiveness, thereby removing the need for degassing steps and reducing production time.
Solution Approach 2:
The patent converts the previously harmful volatile decomposition products into a beneficial water-based system. The silane crosslinking reaction uses water as the byproduct instead of volatile organic compounds, eliminating the need for degassing while maintaining crosslinking efficiency and mechanical properties.
2Temperature
If peroxide crosslinking is used to improve mechanical properties, then heat and deformation resistance are enhanced, but electrical conductivity increases leading to heat generation and thermal runaway risk
Solution Approach 1:
The patent changes the crosslinking chemistry from peroxide-based to silane-based crosslinking. This parameter change fundamentally alters the decomposition products from volatile organic compounds to water, eliminating sources of electrical conductivity degradation while maintaining thermal resistance through effective crosslinking.
Solution Approach 2:
The patent employs a composite approach combining silane-modified polyethylene with crosslinking catalysts. This composite material system achieves both thermal resistance through crosslinking and electrical stability through the absence of conductive decomposition products, resolving the contradiction between heat resistance and electrical stability.
3Strength
If high peroxide content is used to achieve sufficient crosslinking degree, then mechanical strength improves, but volatile by-products increase requiring more extensive degassing
Solution Approach 1:
The patent fundamentally changes the crosslinking mechanism from peroxide decomposition to silane hydrolysis and condensation. This parameter change eliminates volatile by-products entirely while maintaining sufficient crosslinking degree for mechanical strength, as the silane system proceeds through a water-based reaction pathway without generating harmful volatiles.
4Stability of the object's composition
If conventional crosslinking is used to improve deformation resistance, then cable production becomes more complex requiring degassing equipment and procedures
Solution Approach 1:
The patent changes the crosslinking chemistry to a water-based silane system that eliminates volatile by-products. This parameter change simplifies the production process by removing the need for degassing equipment and procedures, reducing device complexity while maintaining deformation resistance through effective crosslinking.
Solution Approach 2:
The silane crosslinking system is self-sufficient, using moisture from the environment or added water as the reaction medium. This self-service characteristic eliminates the need for complex degassing equipment, as the crosslinking reaction proceeds without generating volatile by-products that would require removal.
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 solution provides a balance of low electrical conductivity and robust mechanical properties, reducing heat generation and improving production efficiency, while maintaining high voltage capabilities without the need for degassing, thus addressing the limitations of conventional methods.
Implementation Method 1
Crosslinking can be effected using e.g. a free radical generating compound, such as a peroxide. Free radical generating agent is typically incorporated to the layer material prior to the extrusion of the layer(s) on a conductor. After formation of the layered cable, the cable is then subjected to a crosslinking step to initiate the radical formation and thereby crosslinking reaction.
Implementation Method 2
In crosslinking reaction of a polymer interpolymer crosslinks (bridges) are primarily formed. The polymer material in one or more of said layers is then normally crosslinked to improve e.g. heat and deformation resistance, creep properties, mechanical strength, chemical resistance and abrasion resistance of the polymer in the layer(s) of the cable.
Implementation Method 3
Peroxides are very common free radical generating compounds used i.a. in the polymer industry for said polymer modifications. The resulting decomposition products of peroxides may include volatile by-products which are undesired, since they can be hazardous and may have a negative influence on the electrical properties of the cable. Therefore the volatile decomposition products such as methane e.g. where dicumylperoxide is used, are conventionally reduced to a minimum or removed after crosslinking and cooling step.
Data Source
Figure 1
AI summary
The invention relates to a polymer composition with improved DC electrical properties and to a cable surrounded by at least one layer comprising the polymer composition.