Marine Cable Insulation Structure for Water-Tree Suppression
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Solution Overview
Problem
Marine cables for offshore wind power face challenges in suppressing moisture penetration and diffusion into insulating layers, leading to the formation of water trees, which reduces dielectric strength and shortens lifespan, especially in inter-array cables without a lead sheath layer.
Innovation Solution
A marine cable design featuring a crosslinked polyethylene insulating layer with a degree of crosslinking of 77% or greater and crystallinity of 35% or more, combined with a water-barrier system including inner and outer semiconductive layers, wire shield, and a metallic sheath, along with superabsorbent polymer-based water-barrier tapes, to control water tree size and enhance dielectric strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a lead sheath layer is used to suppress moisture penetration, then water-barrier performance is improved, but flexibility and movement capability deteriorate
Solution Approach 1:
The cable is divided into two types: export cables with lead sheath for fixed seabed installation, and inter-array cables without lead sheath for flexible movement between turbines. This segmentation allows each cable type to be optimized for its specific application requirements.
Solution Approach 2:
Different water-barrier structures are applied to different cable types based on local requirements: export cables receive lead sheath for maximum water protection, while inter-array cables use alternative water-barrier layers that maintain flexibility.
2Adaptability or versatility
If a shield layer formed of metal wires is used instead of lead sheath, then adaptability is improved, but water-barrier performance deteriorates
Solution Approach 1:
A water-barrier layer comprising water-barrier tapes is introduced as an intermediary structure between the semiconductive layer and shield layer in inter-array cables. This water-barrier layer effectively blocks moisture penetration while allowing the cable to maintain flexibility for movement.
3Ease of manufacture
If moisture penetrates into insulating layers, then ease of manufacture is improved, but dielectric strength deteriorates
Solution Approach 1:
Water-barrier layers and water-barrier tapes are incorporated into the cable structure during manufacturing to prevent moisture penetration before it can cause damage. This preliminary protective action ensures long-term dielectric strength without complicating the manufacturing process.
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 limits water tree size to 850 µm or less, achieving a breakdown voltage of 80 kV/mm or higher and extending the lifespan of marine cables by stabilizing insulation performance and preventing moisture-induced degradation.
Implementation Method 1
a degree of crosslinking of the insulating layer is equal to or greater than 77%
Implementation Method 2
a degree of crystallinity of the insulating layer is equal to or greater than 35%
Implementation Method 3
superabsorbent polymer-based water-barrier tapes
Implementation Method 4
suppress penetration and diffusion of moisture into the marine cables
Data Source
Figure 1~2
AI summary
Disclosed is the present invention relates to a marine cable for offshore wind power having an improved water-tree property. More particularly, it relates to a marine cable for offshore wind power, which may effectively suppress formation of water trees caused by diffusion of moisture, having penetrated into cores of the cable, in insulating layers so as to improve dielectric strength and consequently secure a long lifespan.