HV Coil Bushing Joint for Homogeneous Electric Field
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Solution Overview
Problem
Existing combined instrument transformers face challenges in maintaining the integrity of paper-and-oil insulation at the current coil bushing joint, leading to potential weaknesses in the electric field distribution and transformer safety due to protruding threads and edges, and there is a need for improved homogeneity of the electric field within the voltage bushing.
Innovation Solution
The design incorporates an upper screen with rounded edges, made of aluminum cast, positioned at an acute angle to the rod axis, with overlapping equipotential screens and a copper tape for even potential distribution, along with a semiconducting paper external screen, to minimize electric field intensity and enhance transformer quality and safety.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a screw joint is used to connect the current bushing with the joining sleeve, then the assembly is secure, but the protruding threads and edges weaken the paper-and-oil insulation strength
Solution Approach 1:
The harmful protruding threads and edges are removed from the assembly by using a flush-fit design where the bushing and joining sleeve are connected without exposed fastening elements, eliminating the source of insulation weakness while maintaining structural integrity
Solution Approach 2:
The design applies different structural qualities to different regions: the connection interface uses a specialized flush-fit joint to protect insulation, while other parts maintain standard assembly features, optimizing both strength and manufacturability locally
2Reliability
If traditional voltage coil design is used, then the structure is simple, but the electric field distribution is non-uniform
Solution Approach 1:
An equipotential screen is introduced around the voltage coil to create uniform potential distribution, eliminating electric field non-uniformity and improving reliability through controlled electromagnetic environment
Solution Approach 2:
The equipotential screen acts as an intermediary element between the voltage coil and surrounding structures, mediating the electric field distribution to achieve homogeneity without directly modifying the coil winding structure
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
This configuration ensures a more homogeneous electric field, improves the quality of the voltage transformer, and increases the operating safety of the combined instrument transformer by optimizing the distribution of voltage gradients and potential equalization.
Implementation Method 1
the equipotential screens of the bushing are situated in relation to the rod axis in such way that the line connecting the upper edges of the screens located in the insulating material is situated at an acute angle to the rod axis and at the same time it is parallel to the line connecting the bottom edges of these screens
Implementation Method 2
There is also known an external screen made of black semiconducting paper which is located outside the voltage coil and which is electrically connected with the final, wound on the largest diameter, aluminum screen situated on the voltage bushing
Data Source
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AI summary
The invention deals with an HV voltage coil which is an element of a voltage transformer used in a combined instrument transformer applicable in high voltage electric power measuring systems. The voltage coil comprises a magnetic core (16), a primary winding (13) wound onto a secondary winding (14) and surrounded by an upper screen (17), a bushing of a high voltage instrument transformer in the form of a conducting rod (21) placed in insulating material (23) with equipotential screens (25), the primary winding together with the upper screen being located in the coil insulation (24) which is covered by an external screen (26). The voltage coil according to the invention is characterized in that the upper screen (17) has the shape of a ring with a gap (18), which is integrated with a connecting element (19) in the form of a truncated cone. This base of the cone which has the larger diameter is situated on the external surface of the ring, and the cone has an axial opening (20) into which a threaded end of the conducting rod (21) is screwed. Equipotential screens (25) are situated centrically around the rod (21) and they have overlapping longitudinal edges which do not touch one another in any point. A copper tape (27) is wound on the insulation (23) and on the external screen (26) of the voltage coil.