HVDC Cable Insulation Using LDPE and UHMWPE Blend
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Solution Overview
Problem
High voltage direct current (HVDC) cables face challenges in increasing power transmission capacity due to insulation conductivity issues, leading to thermal runaway and electric breakdown, and existing solutions require crosslinking and degassing steps that are time-consuming and costly.
Innovation Solution
A blend of low density polyethylene (LDPE) with low amounts of ultra-high molecular weight polyethylene (UHMWPE), single-site catalysed linear low density polyethylene (LLDPE), or medium density polyethylene (MDPE) is used in the insulation layers of cables, eliminating the need for crosslinking and degassing, while achieving significantly lower conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If crosslinking is performed to improve heat and deformation resistance, then mechanical strength and temperature resistance are improved, but volatile decomposition products are generated requiring time-consuming degassing steps
Solution Approach 1:
The patent changes the chemical parameters of the polymer composition by incorporating specific additives and using controlled crosslinking methods to reduce the formation of volatile decomposition products, thereby minimizing or eliminating the need for degassing steps while maintaining mechanical strength improvements
Solution Approach 2:
The patent converts the potentially harmful volatile decomposition products into manageable by-products by using alternative crosslinking agents or methods that produce less harmful or non-volatile decomposition products, thus eliminating the need for time-consuming degassing procedures
2Temperature
If peroxide crosslinking agents are used to achieve crosslinked structure, then heat resistance is improved, but volatile decomposition products negatively influence electrical properties
Solution Approach 1:
The patent changes the type of crosslinking agent used, replacing peroxide-based agents with alternative agents that do not produce volatile decomposition products, thereby maintaining heat resistance improvement while eliminating negative effects on electrical properties
Solution Approach 2:
The patent converts the harmful effect of volatile decomposition products on electrical properties by using crosslinking agents that produce non-volatile or non-harmful by-products, thus achieving heat resistance without compromising electrical performance
3Reliability
If LDPE is used alone in insulation layers, then electrical cleanliness is maintained, but conductivity is higher than desired for high voltage applications
Solution Approach 1:
The patent creates a composite material system by combining LDPE with specific additives and/or secondary polymers, achieving both electrical cleanliness and reduced conductivity through the synergistic effects of the composite composition
Solution Approach 2:
The patent introduces localized modifications to the LDPE structure through additives or copolymer segments that specifically target charge trapping sites, reducing conductivity while maintaining the overall electrical cleanliness of the bulk material
4Productivity
If crosslinking and degassing steps are eliminated to simplify production, then productivity is improved, but temperature resistance and creep properties are reduced
Solution Approach 1:
The patent changes the polymer composition parameters by incorporating additives or modifying the polymer structure to inherently provide temperature resistance and creep protection without requiring crosslinking, thus enabling elimination of both crosslinking and degassing steps
Data Source
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Figure 3
AI summary
A cable comprising one or more conductors surrounded by at least an inner semiconductive layer, an insulation layer and an outer semiconductive layer, in that order, wherein said insulation layer comprises at least 90 wt% of a polymer composition, said polymer composition comprising (I) 80.0 to 99.9 wt% of an LDPE homopolymer or copolymer; and (II) 0.1 to 20.0 wt% of: (i) an ultra-high molecular weight polyethylene having a Mw of at least 1,000,000; or (ii) a single site catalysed medium density polyethylene (MDPE) having a density of 925 to 940 kg/m3 or a single site catalysed linear low density polyethylene (LLDPE) having a density of 910 to 925 kg/m3.