Compact Transformer Bushing With Removable Insulating End Cap
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Solution Overview
Problem
Existing primary bushings for switchgear and electrical isolation equipment have a larger footprint and higher material costs due to the need for extended length to maintain minimum tracking distances, which is not accommodated by smaller current transformers with smaller inner diameters.
Innovation Solution
A compact bushing design with a removable insulating end cap of larger outer diameter, allowing for increased linear surface distance and shorter shaft length, enabling the use of smaller current transformers and reducing the overall length and footprint of the bushing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the bushing length is extended to maintain minimum tracking distance, then the tracking distance requirement is satisfied, but the footprint and material cost increase
Solution Approach 1:
The patent applies dimensionality change by transitioning from a linear tracking distance approach to a radial/surface path approach. Tracking sheds extend the surface path length radially outward from the bushing axis, allowing the electrical tracking distance to be increased without proportionally increasing the linear bushing length. This creates a multi-dimensional solution where the tracking path exists in both axial and radial dimensions, resolving the contradiction between meeting tracking requirements and minimizing footprint.
Solution Approach 2:
The bushing is segmented into multiple functional sections: a compact main body section with tracking sheds for achieving tracking distance, a conductor section, and a mounting section. This segmentation allows each section to be optimized independently - the tracking sheds provide the required surface distance while the main body remains compact, thus satisfying tracking requirements without increasing overall footprint.
2Reliability
If the bushing length is extended to maintain minimum tracking distance, then the tracking distance requirement is satisfied, but the material cost increases
Solution Approach 1:
By using tracking sheds that extend the surface path in radial and circumferential directions rather than purely axial directions, the patent achieves the required tracking distance with less material volume. The sheds create a longer electrical path through spatial arrangement rather than through increased material quantity, thus reducing material cost while maintaining reliability.
Solution Approach 2:
The patent changes the geometric parameters of the bushing structure by introducing tracking sheds with specific dimensions, angles, and spacing. These parameter changes allow the surface path length to be increased without proportionally increasing the overall bushing dimensions or material quantity, thereby maintaining tracking distance requirements while controlling material cost.
3Quantity of substance
If a smaller current transformer is used with smaller inner diameter, then component cost decreases, but the bushing cannot accommodate the transformer due to insufficient inner diameter
Solution Approach 1:
The bushing is segmented such that the tracking sheds are positioned on the main body section while the conductor section and mounting section maintain a smaller outer diameter. This segmentation allows smaller inner diameter current transformers to be mounted on the bushing, as the critical mounting area does not include the tracking sheds, thus enabling cost reduction while maintaining adaptability.
Solution Approach 2:
Different sections of the bushing have different local qualities - the main body has tracking sheds for electrical performance, while the mounting section has a reduced diameter for mechanical compatibility. This local differentiation allows the bushing to simultaneously satisfy electrical tracking requirements and mechanical mounting requirements for smaller current transformers.
Data Source
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AI summary
A compact electrical bushing (102) has a separate insulating end cap (210) removably attached to the shaft (200) of the bushing at an end used for mounting a current transformer. The removably attached insulating end cap has a large outer diameter that increases the linear surface distance of the bushing. The outer diameter may be determined in a predefined manner based on the desired length of the shaft, and vice versa, with a larger outer diameter corresponding to a shorter shaft. The increased linear surface distance allows the bushing to meet minimum tracking distance with a shorter shaft relative to existing bushings. The shorter shaft reduces the footprint of switchgear and other electrical isolation equipment to which the bushing may be connected. The insulating end cap may be removed from the bushing as needed to allow the current transformer to be slid onto the bushing without having to pass over the end cap.