HVDC Cable Joint Field Grading for Charge Accumulation Control
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Solution Overview
Problem
High voltage direct current (HVDC) cable joints face issues with non-homogeneous electric field distribution and charge accumulation, leading to radial perforation, especially at high voltage levels above 320 kV, where conventional geometric field control methods are insufficient.
Innovation Solution
A joint design featuring a central semiconductive electrode and additional semiconductive electrodes (deflectors) with a longitudinally extending field grading layer, which bridges the boundary between the outer semiconductive layer and the insulation layer, ensuring homogeneous electric field distribution and preventing charge accumulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional geometric field control methods are used in HVDC cable joints, then the joint structure is simple and easy to manufacture, but the electric field distribution becomes non-homogeneous leading to charge accumulation and radial perforation at high voltages above 320 kV
Solution Approach 1:
The joint is divided into multiple functional layers: cable insulation layer, field grading layer, and joint insulation layer. Each layer has a specific thickness and material composition designed to control the electric field distribution. This segmentation allows the complex field control function to be distributed across multiple simpler components, reducing the risk of perforation while maintaining manufacturability.
Solution Approach 2:
The field grading layer is positioned specifically at the interface between cable insulation and joint insulation where electric field concentration occurs. This layer has different material properties (different dielectric constant) than the surrounding insulation layers, creating a localized region that modifies the electric field distribution precisely where needed to prevent charge accumulation and perforation.
2Power
If the voltage level is increased to 320 kV or higher for HVDC systems, then the power transmission capability is improved, but the likelihood of radial perforation due to non-homogeneous electric field distribution increases
Solution Approach 1:
The patent changes the electrical parameters of the joint by introducing a field grading layer with specific dielectric properties. This layer has a different dielectric constant than the surrounding insulation materials, which modifies the electric field distribution pattern. By adjusting the thickness and material composition of this layer, the electric field gradient is controlled to remain homogeneous even at high voltages of 320 kV and above, preventing charge accumulation and perforation while maintaining high power transmission capability.
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 reduces the risk of cable insulating layer perforation by controlling the electric field and gradient, ensuring reliability even at extreme high voltages like 500-600 kV.
Implementation Method 1
the electric field distribution in the interface region between the cable insulating layers and the joint insulating layer can become not homogeneous. This causes a charge accumulation
Implementation Method 2
a layer of material having a non-linear conductivity between the cable insulation layer and the joint insulation layer has been proposed
Data Source
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AI summary
The present invention relates to a joint (100) for high voltage direct current cables (200, 300) extending 5 along a longitudinal axis (X) between two opposite end portions (110, 120), the joint (100) comprising: - a central semiconducting electrode (140); - two semiconducting deflectors (150, 160); - a field grading layer (170) longitudinally extending 10 between each one of the deflectors (150, 160) and the central electrode (140) and in electric contact therewith; - a joint insulating layer (180) surrounding the central electrode (140), the two deflectors (150, 160) 15 and the field grading layer (170); and - a joint outer semiconductive layer (190) surrounding and in direct contact with the insulating layer (180).