High Voltage Current Coil Truncated Cone Guard
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Solution Overview
Problem
The existing high voltage current coils in combined instrument transformers, such as those used in high voltage electric power measuring systems, face issues with the screw joint between the current bushing and the metal enclosure weakening the paper-and-oil insulation due to sharp edges formed by the protruding thread and sleeve, leading to potential partial discharges.
Innovation Solution
A metal protective guard in the shape of a truncated cone is permanently joined to the external surface of the current transformer bushing, covering the screw joint and shielding the insulation from these sharp edges, thereby enhancing the structural integrity and preventing partial discharges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a screw joint is used to connect the current bushing with the metal enclosure, then the assembly is easy to manufacture and disassemble, but the sharp edges formed by the protruding thread and sleeve weaken the paper-and-oil insulation
Solution Approach 1:
A joining sleeve made of insulating material is introduced as an intermediary component between the metal enclosure and the current bushing. This sleeve provides a smooth transition surface that eliminates sharp edges while maintaining the mechanical connection function of the screw joint, thus preserving both ease of assembly and insulation strength
Solution Approach 2:
The paper-and-oil insulation is wrapped around the joining sleeve to provide a continuous insulating layer that conforms to the smooth outer surface of the sleeve, eliminating stress concentrations at sharp edges and maintaining insulation integrity under mechanical stress
2Strength
If the screw joint components are tightly fitted to ensure mechanical strength, then the connection is more robust, but the sharp edges further weaken the surrounding insulation
Solution Approach 1:
The joining sleeve acts as a mediator that distributes mechanical stresses over a larger area, reducing stress concentrations at sharp edges. The insulating material of the sleeve prevents electrical field distortion while maintaining the mechanical strength of the connection
Solution Approach 2:
The smooth outer surface of the joining sleeve and the surrounding paper-and-oil insulation provide a cushioning effect that prevents the formation of sharp edges before they can cause partial discharges, eliminating the harmful effect at its source
Data Source
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AI summary
The invention deals with a high voltage current coil which is an element of a current transformer used in a combined instrument transformer which comprises of a current transformer and a voltage transformer located in a common enclosure. A combined instrument transformer is applicable in high-voltage electric power measuring systems. The current coil according to the invention is distinguished by the fact that it comprises a metal tube (10) which is an element of the current bushing of the current transformer (1), which tube is furnished with a metal protective guard (14) in the shape of a truncated cone whose base with the larger diameter faces a joining sleeve (12), and the edge of the cone base with the smaller diameter is permanently joined with the external surface of the metal tube (10), while the edge of the cone base with the larger diameter is folded inside the cone.