Wall Bushing Grading Ring Geometry for Lower Electric Stress
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Solution Overview
Problem
Existing wall bushings experience high electric stress at the grading ring, particularly in seismic conditions, limiting design flexibility and safety, especially for large gas-insulated bushings.
Innovation Solution
The use of a grading ring with an elliptic cross section, where the major diameter is aligned axially and the minor diameter is radial, reduces electric stress, allowing for higher voltage ratings and more compact designs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a concentric shield is used between the high voltage tube and grounded flange, then electromagnetic requirements on the grounded flange are relaxed, but electric stress at the grading ring increases
Solution Approach 1:
The grading ring is designed with an elliptic cross-section instead of a circular one, creating asymmetric geometry where the major axis is oriented radially. This asymmetric shape redistributes the electric stress field, reducing peak stress concentrations at the grading ring while maintaining the concentric shield configuration's electromagnetic benefits
2Adaptability or versatility
If the high voltage tube is moved to an off-centre position during seismic activity, then movement flexibility is improved, but electric stress on the grading ring increases
Solution Approach 1:
The elliptic cross-section of the grading ring with radial major axis creates an asymmetric stress distribution pattern that better accommodates off-centre positioning during seismic events. The elongated radial dimension provides greater clearance and stress distribution capacity when the high voltage tube shifts from its centred position
3Stability of the object's composition
If support is added between the high voltage tube and grounded shield, then mechanical stability is improved, but isolation is endangered
Solution Approach 1:
The grading ring's cross-sectional parameters are changed from circular to elliptic with specific axis ratios. This parameter change allows the ring to provide enhanced mechanical support and stability to the high voltage tube while maintaining adequate electrical isolation, as the elliptic shape distributes stresses more favorably without requiring additional support structures
Data Source
AI summary
A wall bushing for high voltage application is presented. The wall bushing includes a grounded shield. The grounded shield includes a grading ring in a distal end thereof. The grading ring has an elliptic cross section with conjugate diameters, wherein a major diameter of the conjugate diameters is arranged in an axial direction of the grounded shield and a minor diameter of the conjugate diameters is arranged in a radial direction of the grounded shield. The major diameter is larger than the minor diameter.