Subsea Power Cable Insulation Blend Against Saltwater Water Treeing
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Solution Overview
Problem
Conventional power cables without a moisture impervious layer, or 'wet design' cables, face challenges in saltwater environments due to water treeing, which leads to reduced dielectric strength and potential electric failure, especially in aggressive saltwater conditions where dissolved salts exacerbate the issue.
Innovation Solution
The use of a cable design featuring an insulation layer composed of at least 60 wt% low density polyethylene homopolymer or copolymer with a polyunsaturated comonomer, combined with 10 to 35 wt% low density polyethylene copolymer containing a polar comonomer such as alkyl acrylate or vinyl acetate, along with carbon black in the semiconductive layers, to enhance water tree retardation and resist dielectric breakdown in saltwater environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a moisture impervious layer is added to protect the cable from water ingress, then the cable's protection against water treeing is improved, but the raw material cost and manufacturing expense increase significantly
Solution Approach 1:
The patent removes the moisture impervious layer from the cable construction, transitioning from a dry design to a wet design. Instead of using a separate protective layer, the solution extracts the water barrier function and integrates it directly into the insulation material itself through the polymer blend formulation.
Solution Approach 2:
The patent employs a composite material system in the insulation layer, combining polyethylene base polymer with polymer water tree retarders containing polar groups. This composite approach provides water tree resistance inherently within the insulation material, eliminating the need for separate moisture impervious layers while maintaining cable reliability.
2Reliability
If a moisture impervious layer is used to prevent water ingress, then the cable's resistance to water treeing is improved, but the overall cable cost increases
Solution Approach 1:
The patent merges the functions of the insulation layer and the moisture impervious layer into a single integrated insulation material. The polymer blend with water tree retarders performs both electrical insulation and water resistance functions simultaneously, reducing the total quantity of materials required and lowering overall cable cost.
Solution Approach 2:
By using composite polymer materials with inherent water tree resistance, the patent eliminates the need for additional moisture barrier materials, thereby reducing raw material costs while maintaining water tree protection.
3Ease of manufacture
If conventional polyethylene is used in the insulation layer, then the manufacturing simplicity is maintained, but water trees form under electric fields leading to reduced breakdown strength
Solution Approach 1:
The patent modifies the chemical parameters of the polyethylene insulation material by incorporating polymer water tree retarders with polar groups. This changes the material's chemical composition and polarity, which fundamentally alters its interaction with water and electric fields, preventing water tree formation while maintaining manufacturing simplicity through conventional extrusion processes.
Solution Approach 2:
The patent creates a composite polymer system combining polyethylene with polar water tree retarder polymers. This composite material maintains the ease of manufacturing conventional polyethylene while dramatically improving dielectric breakdown strength by preventing water tree initiation and propagation under electric fields.
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
This design significantly improves the electrical breakdown strength of power cables in saltwater environments, as demonstrated by enhanced performance after wet aging tests, offering a cost-effective and environmentally friendly solution to the challenges of water treeing in wet design cables.
Implementation Method 1
10 to 35 wt% low density polyethylene copolymer containing a polar comonomer such as alkyl acrylate or vinyl acetate, to enhance water tree retardation
Implementation Method 2
carbon black in the semiconductive layers, to enhance water tree retardation and resist dielectric breakdown in saltwater environments
Implementation Method 3
resist dielectric breakdown in saltwater environments
Data Source
AI summary
Use of a cable, e.g. to carry power, in a salt water environment, e.g. in the sea or under the sea; said cable comprising a conductor which is surrounded by at least an inner semiconductive layer, an insulation layer and an outer semi conductive layer in that order; wherein said insulation layer comprises (i) at least 60 wt % of a low density polyethylene homo or low density polyethylene copolymer with at least one polyunsaturated comonomer and optionally one or more further comonomers; and, (ii) 10 to 35 wt % of a low density polyethylene copolymer of ethylene and at least one polar comonomer selected from the group consisting of an alkyl acrylate, an alkyl methacrylate or vinyl acetate.