Cable Termination Field Grading Layer for High Voltage DC
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Solution Overview
Problem
High and extra high voltage cable terminations face premature failure due to non-homogeneous electric field distribution and charge accumulation, often caused by inadequate cable peeling and voids between insulation layers, which increases with voltage levels, especially in DC applications.
Innovation Solution
A cable termination system incorporating semiconducting electrodes and a field grading layer with non-linear conductivity, positioned between the semiconducting electrodes, ensures homogeneous electric field distribution and prevents charge accumulation, simplifying the peeling process and reducing the risk of insulating layer perforation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional stress members are used with traditional cable preparation methods, then the termination assembly can be assembled, but non-homogeneous electric field distribution and charge accumulation occur leading to premature failure
Solution Approach 1:
The patent introduces a field grading layer with non-linear conductivity that changes its electrical properties based on the applied electric field strength. This dynamic parameter change allows the layer to automatically redistribute electric field lines, transforming the non-homogeneous field into a homogeneous distribution and preventing charge accumulation at critical interfaces.
Solution Approach 2:
The termination assembly uses a composite structure combining semiconducting electrodes with a field grading layer having non-linear conductivity characteristics. This composite material system works synergistically to control electric field distribution, where the semiconducting electrodes provide stable potential surfaces and the non-linear conductivity layer dynamically adjusts field distribution based on local field intensity.
2Manufacturing precision
If cable peeling procedures are performed by skilled workers using special tools, then void-free interfaces can be achieved, but the process becomes complex and time-consuming
Solution Approach 1:
The field grading layer is pre-installed on the cable surface before the stress member is fitted. This preliminary action creates a buffer zone that compensates for minor imperfections in cable preparation, reducing the criticality of achieving perfectly void-free interfaces during assembly and simplifying the overall preparation process.
Solution Approach 2:
The field grading layer acts as an intermediary between the cable insulation and the stress member. This intermediate layer absorbs and distributes mechanical stresses and electrical field stresses, reducing the sensitivity of the interface to preparation quality and allowing less stringent peeling procedures while maintaining reliability.
3Ease of operation
If the electric field control element is interference fitted over the prepared cable, then electrical connection is achieved, but inadequate field control leads to charge accumulation and insulating layer perforation
Solution Approach 1:
The field grading layer's non-linear conductivity parameter changes dynamically in response to local electric field intensity. In regions of high field stress, the layer's conductivity increases, drawing more field lines through those regions and redistributing the electric field to prevent charge accumulation and insulating layer breakdown.
Solution Approach 2:
The field grading layer automatically self-regulates electric field distribution without external control. The non-linear conductivity mechanism causes the layer to naturally redirect electric field lines from high-stress regions to lower-stress regions, creating a self-balancing system that maintains field homogeneity and prevents perforation.
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 controls electric field distribution and charge accumulation, reducing the risk of insulating layer perforation and simplifying the peeling process, making it suitable for high and extra high voltage DC applications up to 500-650 kV, and allowing the use of silicone oil as an insulating fluid.
Implementation Method 1
a field grading layer longitudinally extending between the first and second semiconducting electrodes and in electric contact therewith
Implementation Method 2
The combination of semiconducting electrodes arranged as above and the field grading layer affords the due homogeneity of the electric field between the electric field control element and the cable insulating layer
Data Source
AI summary
A cable termination system including a power cable sequentially including a first length of exposed outer semiconductive layer, a length of exposed insulating layer and a length of exposed electric conductor, an electric field control element adapted to be arranged around a portion of said power cable, said electric field control element including: first and second longitudinally spaced semiconducting electrodes; a field grading layer longitudinally extending between the first and second semiconducting electrodes and in electric contact therewith; an insulating layer surrounding the semiconducting electrodes and the field grading layer, wherein the first semiconducting electrode is positioned across a first boundary between the first length of exposed outer semiconductive layer and the length of exposed insulating layer, wherein said second semiconducting electrode is electrically connected with said length of exposed electric conductor, a tubular insulating body adapted to house said power cable and said electric field control element.