Subsea Power Cable Density Control via Composite Armouring
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Solution Overview
Problem
Dynamic sub-sea power cables face mechanical fatigue and water ingress issues due to sea movements, with traditional materials like lead sheaths being prone to cracking and copper sheaths being less dense, leading to excessive cable motion in open sea conditions.
Innovation Solution
Incorporating a density-raising element with a higher density than the protective sheath, such as lead, copper, or steel, to increase the cable's density and stability, thereby reducing excessive motion caused by sea currents and waves.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a copper sheath is used as the protective sheath, then the mechanical fatigue resistance is improved, but the cable density decreases leading to excessive cable motion in open sea
Solution Approach 1:
The patent uses a composite structure combining copper sheath (for fatigue resistance) with steel wire armouring (for density and mechanical strength). The copper sheath provides corrosion resistance and fatigue strength, while the steel armouring layers add density and tensile strength to prevent excessive cable motion in open sea conditions.
Solution Approach 2:
The patent implements a nested structure where the copper sheath surrounds the conductors, and steel wire armouring is nested around the copper sheath. This multi-layer nested configuration allows each material to perform its specific function while contributing to the overall cable performance.
2Weight of moving object
If a lead sheath is used as the protective sheath, then the cable density is increased preventing excessive motion, but the mechanical fatigue strength decreases leading to cracking
Solution Approach 1:
The patent replaces the traditional lead sheath with a composite structure using copper sheath for fatigue resistance and steel wire armouring for density. This composite approach eliminates the drawbacks of lead while maintaining the benefits of high density and mechanical strength.
Solution Approach 2:
The patent extracts the density function from the lead sheath and assigns it to the steel wire armouring, while the copper sheath is dedicated to providing fatigue resistance and corrosion protection. This functional separation allows each component to optimize its specific performance.
3Ease of operation
If the cable is allowed to move freely with sea motions, then the cable flexibility is improved, but mechanical fatigue occurs due to repeated movements
Solution Approach 1:
The combination of copper sheath and steel wire armouring creates a composite structure that balances flexibility and fatigue resistance. The copper sheath allows the cable to bend and move with sea motions, while the steel armouring reinforces the cable to resist fatigue from repeated movements.
Solution Approach 2:
The copper sheath acts as a flexible protective layer that allows the cable to accommodate sea motions while the steel wire armouring provides the necessary mechanical strength to prevent fatigue failure.
Data Source
AI summary
An electric power cable including at least one electric conductor. An electric insulation surround the conductor and includes a polymer. A tubular protective sheath surrounds the electric insulation and acts as a water barrier that prevents water intrusion into the electric insulation. The protective sheath includes a metal as a main constituent. The cable includes at least one density-raising element of a material of higher density than the material of the protective sheath, in order to increase the density of the cable such that too large motions thereof are prevented when the latter is installed in open sea.