Rigid Joint Assembly Insulation Deformation Prevention
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Solution Overview
Problem
Existing rigid joint assemblies for submarine cables fail to maintain insulation integrity at water depths greater than 600 meters due to excessive deformation and pressure gradients, leading to necking and compromised electrical characteristics.
Innovation Solution
A rigid pipe is used to surround the cable core end section at the cable entry part of the casing assembly, preventing deformation and displacement by locking the insulation system in place and maintaining continuous contact, thereby protecting the insulation from pressure differences and mechanical stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a regular rigid joint is used for submarine cables at large water depths, then the joint structure is simple and easy to manufacture, but excessive deformation and necking of the cable insulation occurs due to pressure gradients
Solution Approach 1:
A rigid support member is introduced as an intermediary element between the cable core and the pressure environment. This support member acts as a mediator that directly resists the external hydrostatic pressure and prevents it from acting on the cable insulation, thereby eliminating necking and deformation while maintaining the simplicity of the overall joint structure.
Solution Approach 2:
The rigid support member is positioned in advance within the cable entry part of the casing assembly to preemptively counteract the harmful effects of pressure gradients. By having the support member already in place before the cable is subjected to deep-sea pressure, it prevents deformation and necking from occurring in the first place, rather than attempting to correct them afterward.
2Device complexity
If the cable core is exposed to high hydrostatic pressure outside the casing, then the joint structure remains simple, but the insulation system undergoes plastic deformation, yielding and creep
Solution Approach 1:
The rigid support member serves as a protective intermediary that shields the cable insulation from direct exposure to hydrostatic pressure. It absorbs and resists the external pressure forces, preventing them from acting on the insulation system and thereby maintaining the insulation's mechanical strength and preventing plastic deformation, yielding, and creep.
Solution Approach 2:
The rigid support member is installed in advance within the cable entry part to provide preemptive protection against pressure-induced deformation. It acts as a cushioning element that is already in position to absorb and distribute the hydrostatic pressure before it can affect the cable insulation, thereby preventing strength degradation.
3Temperature
If the cable insulation is heated during operation, then the electrical characteristics are maintained, but the mechanical strength of the extruded insulation is reduced making it more susceptible to deformation
Solution Approach 1:
The rigid support member acts as a stable intermediary structure that maintains the cable core's positional stability even when the insulation is heated. While heating occurs to maintain electrical characteristics, the rigid support member prevents the softened insulation from deforming or moving, thereby maintaining structural stability during thermal operation.
Solution Approach 2:
The rigid support member is positioned in advance to counteract the destabilizing effect of heating on the insulation. When the insulation is heated and its mechanical strength is temporarily reduced, the pre-positioned rigid support member immediately prevents deformation, providing preliminary anti-action against the instability caused by temperature increase.
4Reliability
If a rigid support member is added to prevent insulation deformation, then insulation integrity is maintained, but the joint assembly complexity increases
Solution Approach 1:
Instead of making the entire joint assembly complex, the rigid support member is applied locally only in the cable entry part where the pressure gradient and deformation risk are most severe. This localized approach provides the necessary insulation protection while minimizing the increase in overall joint assembly complexity, as other parts of the joint remain unchanged.
Solution Approach 2:
The joint assembly is segmented into distinct functional parts, with the rigid support member being a separate, modular component installed specifically in the cable entry part. This segmentation allows the support member to be added as an independent element without redesigning the entire joint assembly, thereby limiting the increase in complexity to a single modular component rather than the whole system.
Data Source
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AI summary
A rigid joint assembly comprising a first cable core end section (12) of a first electric cable (10), and a second cable core end section (112) of a second electric cable (110), said respective first and second cable core end section comprising an electrical cable core comprising at least an inner electric conductor (14), and an insulation system comprising at least an inner semi-conducting layer (15), an insulation layer (16) and an outer semi-conducting layer (17). The rigid joint assembly further comprises a joint connection (20) inside which the electrical cable core of the first cable core end section is jointed with the electrical cable core of the second cable core end section, and a water tight metal casing assembly (30) surrounding the joint connection. The casing assembly has a first cable entry part (32) comprising an opening (34) for receiving the first cable core end section and a second cable entry part (132) comprising an opening (134) for receiving the second cable core end section. The rigid joint assembly further comprises a first cable insulation system deformation preventing member (40) that surrounds the first cable core end section (12) at the first cable entry part (32) and a second cable insulation system deformation preventing member (140) that surrounds the second cable core end section (112) at the second cable entry part (132), and the respective deformation preventing member (40; 140) comprises a rigid pipe (41) that surrounds the respective cable core end section at the respective cable entry part.