Submarine Cable Armour Transition for Thermal Management
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Solution Overview
Problem
Submarine electric cables face reduced current carrying capacity due to magnetic hysteresis and eddy current losses in the armour materials, particularly in sections with challenging thermal conditions, leading to increased heat generation and potential cable damage, which existing solutions either increase cable size or cost, or complicate installation with transition joints.
Innovation Solution
The cable is designed with sections of armour made from ferromagnetic materials like carbon steel in standard conditions and non-ferromagnetic materials like stainless steel in critical sections, with anticorrosion measures such as zinc rods or strips at transitions to minimize losses and prevent corrosion, maintaining uniform cable structure and handling characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If ferromagnetic armour material (carbon steel) is used in sections with challenging thermal conditions, then mechanical strength and resistance against external damage are improved, but magnetic hysteresis and eddy current losses increase leading to heat generation and reduced current carrying capacity
Solution Approach 1:
The patent applies different armour materials to different sections of the cable based on local requirements. Ferromagnetic carbon steel armour is used in standard conditions where mechanical strength is prioritized, while non-ferromagnetic stainless steel armour is used in sections with challenging thermal conditions where energy loss must be minimized. This local differentiation resolves the contradiction by matching material properties to specific operational environments along the cable route.
Solution Approach 2:
The patent changes the material parameter of the armour from ferromagnetic to non-ferromagnetic in specific sections. By selecting stainless steel with different magnetic properties for sections experiencing higher temperatures or poorer thermal dissipation, the patent modifies the fundamental material parameter to eliminate magnetic hysteresis losses while maintaining adequate mechanical protection.
2Loss of energy
If non-ferromagnetic armour material (stainless steel) is used in critical sections, then magnetic hysteresis losses are reduced improving current rating, but corrosion resistance requirements increase
Solution Approach 1:
The patent employs a composite armour structure where stainless steel wires are combined with galvanised steel elements. The stainless steel provides non-ferromagnetic properties to reduce magnetic hysteresis losses, while the galvanised steel components contribute enhanced corrosion resistance through zinc coating. This composite approach allows the armour to simultaneously achieve both low energy loss and high reliability against corrosion in challenging environments.
3Ease of operation
If uniform cable structure is maintained through armour transition, then handling characteristics and installation simplicity are preserved, but transition zone corrosion protection complexity increases
Solution Approach 1:
The patent introduces an intermediary protective layer of galvanised steel elements at the transition zones between different armour materials. This intermediate layer acts as a mediator that provides uniform corrosion protection across the transition area, preventing direct contact between dissimilar metals that could cause galvanic corrosion. The galvanised coating serves as a sacrificial barrier that simplifies the transition design while maintaining protection effectiveness.
4Quantity of substance
If cable armour is optimized for thermal sections, then current rating is maintained without increasing cable size, but armour material cost increases
Solution Approach 1:
The patent segments the cable armour into multiple sections along its length, with each section using armour material optimized for its specific operational conditions. Rather than using expensive non-ferromagnetic stainless steel armour throughout the entire cable, the patent applies it only to specific sections with challenging thermal characteristics. This segmentation allows the cable to maintain current rating in critical sections while using more economical carbon steel armour in standard sections, thereby controlling overall manufacturing cost.
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 approach reduces heat losses and maintains cable current rating without increasing overall cable size or cost, simplifying installation by avoiding complex transitions and ensuring mechanical integrity, while effectively managing thermal challenges in specific sections.
Implementation Method 1
the magnetic field generated by the current flowing in the conductor/s induces losses in ferromagnetic materials, such as low to medium carbon-containing steel used as armour wires. The magnetic domains of the ferromagnetic material rotate with the magnetic field in alternate current cable. This rotation of magnetic domains in the material causes friction and heat. The heat produced by this friction is called magnetic hysteresis loss.
Implementation Method 2
Another phenomenon possibly affecting the current rating of a cable is that of the eddy currents. In an AC cable eddy currents are induced in conductive material, such as the metal of the cable armour. Eddy currents cause energy to be lost in form of heat
Implementation Method 3
Galvanized steel is preferably used when the armour wires are exposed to the environment without any polymeric sheath or yarn layer, to ensure better resistance to corrosion.
Data Source
AI summary
An electric power transmission cable (200,300) comprising: at least one first section (235;335) provided with cable armour (355a) made of a first metallic material, and at least one second section (225;325) provided with a cable armour (355b) made of a second metallic material, wherein the second metallic material has ferromagnetic properties substantially lower than those of the first metallic material.