Electric Cable With Electrical Property Gradient Layer
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Solution Overview
Problem
Medium and high voltage power cables experience degradation due to 'water treeing' caused by humidity and electric fields, leading to electrical breakdown and reliability issues in power transmission networks.
Innovation Solution
An electric cable with a layer having an electrical property gradient, comprising a polymeric composition with conductive carbonaceous fillers, where the electrical conductivity and/or dielectric permittivity gradually decrease from the internal to the external surface, forming a percolating network that limits space charge-induced degradation and enhances resistance to breakdown in humid environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a uniform insulating layer is used in power cables, then the manufacturing process is simple, but the resistance to breakdown in humid environments deteriorates due to water treeing caused by space charge accumulation at interfaces
Solution Approach 1:
The patent applies local quality by creating a radially non-uniform insulating layer where the electrical properties (conductivity and/or permittivity) vary continuously from the inner surface near the conductor to the outer surface. This gradient structure allows different regions of the same layer to have different electrical characteristics, preventing space charge accumulation at sharp interfaces while maintaining a single-layer configuration.
Solution Approach 2:
The patent implements parameter changes by modifying the electrical conductivity and/or permittivity parameters radially across the insulating layer. The continuous variation of these parameters creates a gradient that eliminates abrupt property discontinuities, thereby preventing water treeing and improving breakdown resistance without requiring multiple discrete layers.
2Reliability
If multiple layers with different conductive polymer contents are used to prevent water treeing, then the resistance to aging in humid environments improves, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent merges the functions of multiple discrete layers into a single continuous insulating layer with a radial property gradient. Instead of manufacturing separate layers with different conductive polymer contents and assembling them, the invention creates one integrated layer where properties vary continuously, simplifying manufacturing while achieving the same protective effect against water treeing.
Solution Approach 2:
The single insulating layer incorporates local quality variations through its radial gradient structure, where different regions have different electrical properties optimized for their specific locations. This eliminates the need for multiple uniform layers with different compositions, reducing manufacturing complexity while maintaining the ability to prevent water treeing throughout the cable structure.
3Stability of the object's composition
If conventional three-layer insulation (internal semi-conductive/electrically insulating/external semi-conductive) is used, then the cable structure is well-established, but discontinuities in electrical properties lead to space charge accumulation and electrical tree growth under electric fields
Solution Approach 1:
The patent applies parameter changes by transitioning from a multi-layer structure with abrupt property discontinuities to a single layer with continuous radial parameter variation. The electrical conductivity and/or permittivity change gradually across the layer thickness, eliminating the sharp interfaces that cause space charge accumulation and subsequent electrical treeing in conventional cables.
Solution Approach 2:
The insulating layer functions as a composite material with spatially varying composition, where the conductive polymer content or polymer type varies radially to create the desired property gradient. This composite structure combines the benefits of different materials throughout a single continuous phase, avoiding the interface problems of layered composites.
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 electrical property gradient layer effectively prevents degradation caused by space charges and improves the cable's resistance to breakdown under both AC and DC voltage, replacing the need for multilayer insulation with a simpler, easier-to-implement monolayer design.
Implementation Method 1
forming a percolating network that limits space charge-induced degradation and enhances resistance to breakdown in humid environments
Data Source
Figure 1~2
AI summary
The cable (1) has a layer (3) with an electrical property gradient surrounding a central lengthened electric driver (2). The layer includes a zone (3c) located between an inner surface (3a) and an outer surface (3b). The zone includes an electrical conductivity and/or a dielectric permittivity lower than electrical conductivities and/or dielectric permitvities of the inner surface and the outer surface. The layer is obtained from a polymeric composition including polymer and electrically conducting filling material e.g. carbonaceous filling material. The carbonaceous filling material is carbon black, carbon fiber, graphite, graphene, fullerene, carbon nanotube, or mixture. An independent claim is also included for a method for manufacturing a layer with an electrical property gradient.