Ultra-High Voltage DC Power Cable Insulation Design
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Solution Overview
Problem
Ultra-high voltage DC power cables face issues with electric field concentration, partial discharge, and dielectric breakdown due to oil-free voids in the insulating layer, which reduces their lifespan and productivity, especially in long-distance and submarine applications.
Innovation Solution
A power cable design featuring a structured insulating layer with inner and outer kraft paper layers cross-wound with semi-synthetic paper, impregnated with high-viscosity insulating oil, and a metal sheath to evenly distribute electric fields and prevent void formation, combined with a specific winding pattern and layer thickness to enhance flexibility and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If insulating paper is cross-wound with gaps to improve productivity and flexibility, then cable manufacturing efficiency increases and flexibility improves, but electric field concentration occurs in the gaps leading to partial discharge and dielectric breakdown
Solution Approach 1:
The patent applies local quality by using different paper types in different locations: semi-synthetic paper with higher resistivity is placed in the intermediate insulating layer where gaps occur, while kraft paper is used in inner and outer layers. This localized material differentiation ensures that gaps are filled with high-resistivity material to prevent electric field concentration, while maintaining the overall gap-winding structure for productivity and flexibility.
Solution Approach 2:
The patent employs composite materials by combining kraft paper and semi-synthetic paper in a multi-layer structure. The semi-synthetic paper (comprising cellulose fibers and thermoplastic resin) is specifically used in the intermediate layer to fill gaps and provide high resistivity, while kraft paper provides structural integrity. This composite approach resolves the contradiction by integrating materials with complementary properties.
2Reliability
If gap width is reduced to prevent electric field concentration, then dielectric strength improves, but manufacturing efficiency decreases and cable flexibility is reduced
Solution Approach 1:
Instead of uniformly reducing gap width throughout the insulating layer, the patent applies local quality by maintaining larger gaps in the intermediate insulating layer and filling them with semi-synthetic paper. This localized approach prevents electric field concentration at gap locations while preserving overall gap dimensions that enable efficient manufacturing and cable flexibility.
3Reliability
If insulating oil viscosity is increased to prevent oil movement and void formation, then dielectric strength improves, but oil impregnation efficiency decreases
Solution Approach 1:
The patent applies preliminary action by performing vacuum impregnation before the cable is put into service. This preliminary impregnation process ensures that high-viscosity insulating oil thoroughly penetrates the insulating paper layers and fills all gaps and voids before the cable operates. The vacuum condition facilitates oil penetration despite high viscosity, and once impregnated, the oil remains stationary to prevent void formation during operation.
4Reliability
If multi-layer cross-winding structure is implemented to improve dielectric strength, then electric field distribution improves, but structural complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the insulating layer into three distinct functional layers: inner insulating layer (kraft paper), intermediate insulating layer (semi-synthetic paper), and outer insulating layer (kraft paper). Each layer serves a specific purpose: inner and outer layers provide structural integrity and electric field management, while the intermediate layer specifically addresses gap-related issues. This segmented approach improves electric field distribution while maintaining manageable structural complexity through clear functional differentiation.
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 effectively alleviates electric field concentration, suppresses partial discharge and dielectric breakdown, thereby increasing the cable's lifespan and productivity while maintaining flexibility and structural stability, suitable for long-distance and submarine applications.
Implementation Method 1
an insulating layer covering the inner semi-conductive layer and impregnated with an insulating oil
Implementation Method 2
Power cables employing a polymeric insulator, such as cross-linked polyethylene (XLPE), as an insulating layer have been used
Data Source
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Figure 3~4
AI summary
Provided is a power cable, particularly, an ultra-high voltage underground or submarine cable for long-distance direct-current transmission. Specifically, the present invention relates to a power cable which includes an insulating layer of high dielectric strength, is capable of uniformly and effectively alleviating an electric field applied to the insulating layer, is particularly structurally stable, has high flexibility, and is capable of suppressing partial discharge, dielectric breakdown, etc. of the insulating layer, thereby increasing the lifespan and productivity of the cable.