LDPE/HDPE Cable Insulation for Low-Conductivity HVDC Operation
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Solution Overview
Problem
Existing cable insulation materials face challenges in achieving low electrical conductivity and mechanical stability, particularly in high voltage direct current (HVDC) cables, which require increased voltage levels, leading to thermal runaway and mechanical breakdown due to the presence of catalyst residues and peroxide decomposition products.
Innovation Solution
A blend of low density polyethylene (LDPE) with low amounts of high density polyethylene (HDPE) is used in the insulation layer, eliminating the need for crosslinking agents and degassing steps, resulting in a thermoplastic composition with significantly reduced conductivity and improved mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If crosslinking agents are used to improve mechanical strength and temperature resistance, then the cable insulation layer gains better thermomechanical properties, but peroxide decomposition products and catalyst residues cause increased electrical conductivity and mechanical breakdown
Solution Approach 1:
The invention extracts and removes the harmful crosslinking agents and catalyst residues from the cable insulation layer by using a silane-modified polyethylene composition that cures through moisture-induced hydrolysis and condensation rather than peroxide crosslinking, thereby eliminating peroxide decomposition products and catalyst residues that cause electrical conductivity issues
Solution Approach 2:
The invention changes the chemical composition parameters by incorporating silane-modified polyethylene with specific silane group content (0.1-10 mmol/g) and controlling the water content (0.01-5 wt%) to enable alternative crosslinking mechanism that does not produce harmful decomposition products
2Temperature
If peroxide crosslinking is performed to improve heat and deformation resistance, then the insulation layer gains better thermal stability, but volatile by-products require time-consuming degassing steps that reduce productivity
Solution Approach 1:
The invention incorporates water-sensitive silane groups into the polyethylene structure before extrusion, which then react with moisture during or after extrusion to form crosslinks, eliminating the need for separate peroxide crosslinking and degassing steps
Solution Approach 2:
The invention replaces the peroxide-based chemical crosslinking system with a moisture-induced silane crosslinking system, substituting the harmful peroxide decomposition mechanism with a cleaner hydrolysis and condensation reaction that does not produce volatile by-products requiring degassing
3Power
If higher voltage levels are applied to increase power transmission capability, then the power transmission capability is improved, but thermal runaway and mechanical breakdown occur due to insulation heating from leakage current
Solution Approach 1:
The invention changes the electrical conductivity parameter of the insulation layer by using ultra-high molecular weight polyethylene with controlled crystallinity and silane modification, achieving lower conductivity that reduces leakage current and heat generation at high voltage levels
Solution Approach 2:
The invention creates a composite material system combining ultra-high molecular weight polyethylene with silane modifiers and controlled water content, producing a multi-phase structure with improved electrical and thermal properties that prevents thermal runaway at high voltage operating conditions
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 LDPE/HDPE blend achieves lower conductivity and reduced mechanical breakdown risk, enabling faster, less complex, and cost-effective cable production capable of operating at higher voltages without thermal runaway.
Implementation Method 1
The composition comprises 98.0 to 99.9 wt% of a silane-modified polyethylene and 0.1 to 5.0 wt% of water, wherein the silane-modified polyethylene and water are capable of forming crosslinks through moisture-induced hydrolysis and condensation reactions
Implementation Method 2
the silane-modified polyethylene and water are capable of forming crosslinks through moisture-induced hydrolysis and condensation reactions
Implementation Method 3
the combination of low amounts of HDPE and LDPE leads to remarkable conductivity reduction in thermoplastic and cross-linked insulation layers
Data Source
AI summary
A cable comprising a conductor surrounded by at least an inner semiconductive layer, an insulation layer and an outer semiconductive layer, in that order, wherein the insulation layer is not crosslinked or is cross-linked and comprises at least 90 wt% of a polymer composition, said polymer composition comprising: (I) 95.5 to 99.9 wt% of an LDPE; and (II) 0.1 to 4.5 wt% of an HDPE having a density of at least 940 kg/m3.