Top-Tensioned Tendon Cable Support for Offshore HVDC Cooling
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Solution Overview
Problem
Offshore natural gas transportation via vessels or pipelines is costly and inefficient, and existing high-voltage direct current (HVDC) power cables face fatigue and thermal issues due to dynamic applications and heating, limiting power transmission.
Innovation Solution
An offshore production system that converts natural gas to electrical power and transmits it through HVDC power cables with a top-tensioned riser and cooling systems, including a surface pump and subsea cooling joints, to reduce fatigue and thermal expansion, using a connector assembly with potting material to manage dynamic loads and a cooling system for natural convection or forced convection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If HVDC power cables are used for offshore power transmission, then electrical power can be transmitted from the surface structure to the seabed, but the cables experience fatigue and thermal expansion due to dynamic applications and heating
Solution Approach 1:
The electrical cable is nested within the tubular tendon structure, which provides mechanical protection and support. The cable passes through the central passage of the tendon, allowing the cable to benefit from the structural integrity of the outer tendon while maintaining electrical function
Solution Approach 2:
The tubular tendon acts as an intermediary structure between the surface vessel and seabed equipment. It provides a protected pathway for the electrical cable, isolating the cable from direct exposure to dynamic environmental forces while still allowing power transmission
2Temperature
If cooling fluid is pumped through the central passage of the tubular tendon, then the electrical cable can be cooled to prevent overheating, but additional equipment and complexity are required
Solution Approach 1:
The central passage of the tubular tendon serves multiple functions: it provides structural support for the tendon itself, and simultaneously acts as a cooling channel for the electrical cable. This multi-functional design allows cooling capability to be integrated into the existing tendon structure rather than requiring separate cooling infrastructure
Solution Approach 2:
A hydraulic cooling system is implemented by pumping cooling fluid through the central passage of the tubular tendon. The fluid flow removes heat from the electrical cable, preventing thermal damage while the system integrates with the existing tendon structure
3Strength
If a connector is used to physically support the electrical cable in the upper connection system, then the cable can be securely attached, but the connector and potting material add complexity to the connection system
Solution Approach 1:
The connector assembly merges multiple functions into a single integrated structure: it provides mechanical attachment of the cable, structural support through the tendon connection, and environmental sealing through potting material. This consolidation reduces the number of separate components needed while maintaining attachment strength
Solution Approach 2:
The connection system uses composite construction with the tubular tendon providing structural strength, the connector providing mechanical attachment, and potting material providing sealing and additional support. This composite approach achieves strong cable attachment while integrating multiple protective functions
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 system reduces the fatigue of power cables, minimizes thermal expansion, and increases the efficiency and longevity of electrical power transmission from an offshore platform to the seabed, eliminating the need for gas pipelines and reducing material damage from excessive heating.
Implementation Method 1
a pump configured to pump fluid through the central passage of the tubular tendon to cool the electrical cable
Implementation Method 2
a cooling joint disposed subsea and coupled to the tendon, wherein the cooling joint comprises a first port configured to allow sea water to enter a passage of the cooling joint and a second port spaced from the first port configured to vent sea water from the passage and cool the electrical cable through natural convection
Implementation Method 3
tubular tendon extending between the surface vessel and a lower connection system disposed at a seabed, the riser coupled to the surface vessel with an upper connection system
Data Source
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AI summary
An offshore production system includes a surface vessel, a tubular tendon extending between the surface vessel and a lower connection system disposed at a seabed, the riser coupled to the surface vessel with an upper connection system, and an electrical cable extending through a central passage of the tubular tendon, wherein the upper connection system comprises a connector that physically supports the electrical cable.