Oil-Filled HVDC Cable Insulation for Low-Temperature Void Suppression
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Solution Overview
Problem
Ultra-high voltage power cables face issues with partial discharge and dielectric breakdown due to large voids forming in the insulating layer when exposed to low temperatures for extended periods, especially in submarine and underground applications, where the insulating oil shrinks and concentrates electric fields.
Innovation Solution
A power cable design featuring a specific configuration of insulating and semi-conductive layers, with a medium- or high-viscosity insulating oil, and a controlled thickness of the outer semi-conductive layer to prevent void formation, ensuring the insulating oil remains within the outer semi-conductive layer and reducing electric field concentration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a power cable is installed in a low-temperature environment and left for a long time before current supply, then the insulating oil shrinks and forms large voids in the insulating layer, but this causes electric field concentration leading to partial discharge and dielectric breakdown
Solution Approach 1:
The patent applies preliminary anti-action by providing a specific minimum thickness for the outer semi-conductive layer (7.5 to 15% of total thickness) that prevents void formation in advance. This structural design counteracts the shrinkage of insulating oil at low temperatures before it can cause harmful electric field concentration and partial discharge, thereby maintaining cable reliability without requiring active monitoring or intervention.
Solution Approach 2:
The patent changes the structural parameter of the outer semi-conductive layer thickness to a specific range (7.5 to 15% of total thickness) to optimize performance. This parameter adjustment ensures that the layer is thick enough to prevent void formation and electric field concentration, yet thin enough to maintain overall cable efficiency, resolving the contradiction between reliability and harmful electric field effects.
2Volume of moving object
If the outer semi-conductive layer is made thinner to reduce cable size, then cable dimensions are reduced, but voids may extend into the insulating layer causing partial discharge
Solution Approach 1:
The patent identifies and optimizes the critical parameter of outer semi-conductive layer thickness, setting it to a specific range (7.5 to 15% of total thickness). This precise parameter control allows the layer to be thin enough to reduce overall cable dimensions while simultaneously thick enough to contain voids within itself and prevent their extension into the insulating layer, thus maintaining reliability.
Solution Approach 2:
The patent applies local quality by concentrating the void-containing outer semi-conductive layer at the cable periphery, away from the critical insulating layer. This localized placement of potential defects in the outer layer protects the inner insulating layer from electric field concentration and partial discharge, enabling thinner overall cable design without compromising reliability.
3Reliability
If the outer semi-conductive layer is made thicker to prevent void formation, then void containment is improved, but cable outer diameter increases
Solution Approach 1:
The patent optimizes the outer semi-conductive layer thickness to a specific range (7.5 to 15% of total thickness) that achieves the minimum required for void containment while minimizing unnecessary material usage. This optimized parameter prevents both under-thickening (which would allow void extension) and over-thickening (which would unnecessarily increase cable diameter), resolving the contradiction between reliability and volume.
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
The solution effectively increases the cable's dielectric strength and lifespan by preventing partial discharge and dielectric breakdown, even when the cable is installed in low-temperature environments and subjected to long-term storage before current supply.
Implementation Method 1
when the cable is left at low temperatures for a long time until electric current is supplied thereto after installed in a low-temperature environment... the insulating oil shrinks and concentrates electric fields
Implementation Method 2
a temperature change occurs inwardly in a radial direction... due to heat generated due to a joule loss... the viscosity of the insulating oil in the portion of the insulating layer adjacent to the inner semi-conductive layer having relatively high temperature decreases and thus the insulating oil thermally expands and moves
Implementation Method 3
heat generated due to a joule loss due to the electric current flowing through a conductor of the cable
Data Source
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AI summary
Provided is a power cable, particularly, an ultra-high voltage underground or submarine cable for long-distance direct-current transmission. More specifically, the present invention relates to a power cable, in which an insulating layer has high dielectric strength, an electric field applied to the insulating layer is effectively reduced, and particularly, a large void is suppressed from occurring in the insulating layer when the power cable is left at low temperatures for a long time until electric current is supplied thereto after installed in a low-temperature environment, thereby effectively preventing partial discharge, dielectric breakdown, etc. from occurring due to an electric field concentrated in the large void.