Electrical Bushing Foil Edge Field Grading
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Solution Overview
Problem
High voltage bushings face limitations in voltage-withstanding properties due to local electric field enhancements at the edges of coaxial foils, which restrict the operational voltage and require larger diameters, making it challenging to increase voltage ratings within limited physical spaces.
Innovation Solution
Incorporating a Field Grading Material (FGM) part made from non-linear field grading materials, arranged in the extension of conductive foil edges, which provides efficient field grading by reducing electric field strength at the edges, allowing for improved voltage-withstanding properties while maintaining or reducing the bushing diameter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional coaxial foils are used for capacitive grading, then efficient field grading is achieved, but local field enhancement at foil edges limits operational voltage
Solution Approach 1:
The patent applies local quality by introducing FGM parts specifically at the foil edges where field enhancement occurs, rather than uniformly throughout the structure. The FGM material properties (non-linear conductivity or permittivity) are localized to the regions experiencing highest electric field stress, providing targeted field grading exactly where needed to eliminate the harmful edge effects while maintaining the overall capacitive grading structure.
Solution Approach 2:
The patent employs composite materials by combining conventional conductive foils with Field Grading Material parts at the foil edges. The FGM represents a composite material system that integrates materials with different electrical properties (conductive foil material + FGM material) to achieve superior field distribution characteristics that neither material could provide alone, thereby resolving the local field enhancement problem.
2Reliability
If techniques to reduce field stress at foil edges are applied, then voltage-withstanding properties improve, but bushing diameter increases
Solution Approach 1:
The FGM parts are localized specifically at the foil edges rather than being distributed throughout the entire bushing structure. This local application provides the necessary field stress reduction exactly where needed (at the edges) without requiring a uniform increase in bushing dimensions, thereby improving voltage-withstanding capability while maintaining compact overall dimensions.
Solution Approach 2:
The patent changes the electrical parameters (conductivity or permittivity) of the FGM parts in response to the local electric field conditions. The non-linear electrical characteristics of the FGM allow the material to provide enhanced field grading capability at high field regions (foil edges) while maintaining appropriate field distribution in other regions, achieving improved voltage-withstanding without proportional increase in bushing diameter.
3Reliability
If higher voltages are employed to meet advancing electric power technology requirements, then voltage ratings increase, but the relationship between voltage-withstanding properties and bushing diameter deteriorates
Solution Approach 1:
The patent utilizes parameter changes by employing FGM with non-linear electrical characteristics that adapt to different voltage levels. The FGM's conductivity or permittivity changes in response to the applied electric field strength, allowing the bushing to effectively handle higher voltages without requiring proportional increases in diameter, thus maintaining an favorable voltage-to-diameter relationship even as voltage ratings increase to meet advancing power technology requirements.
Solution Approach 2:
By incorporating FGM parts into the conventional foil structure, the patent creates a composite grading system that enhances the voltage-withstanding capability per unit diameter. The combination of conductive foils and FGM materials provides superior field control that enables higher voltage ratings within the same or reduced bushing dimensions, improving the voltage-to-diameter relationship.
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 use of FGM parts effectively reduces electric field stress at the edges, enabling higher voltage ratings without increasing bushing diameter, thus enhancing the relationship between voltage-withstanding capabilities and physical dimensions, while minimizing the risk of partial discharges and bushing failure.
Implementation Method 1
The FGM part and the conductive foil, in the extension of which the FGM part is arranged, are in electrical contact. Furthermore, the FGM part extends beyond at least part of the conductive foil edge over an extension distance (dE), where the extension distance lies within a range of four times an interfoil separation distance of the bushing or less. The electrical field at the foil edge will thus be graded by the FGM part at local electric field strengths above the electric field threshold of the field grading material.
Data Source
Figure 1
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Figure 3a~3c
AI summary
An electrical bushing for providing electrical insulation of a conductor extending through the bushing is disclosed. The bushing comprises: at least one conductive foil concentrically arranged around the conductor location; and at least one FGM part, made from a field grading material and at least partly arranged in the extension of at least part of a foil edge (205/405) of a conductive foil. The FGM part and the conductive foil, in the extension of which the FGM part is arranged, are in electrical contact.