Wound Core Surface Geometry for Transformer Heat Dissipation
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Solution Overview
Problem
The temperature rise of iron cores and winding wires in transformers is difficult to control due to heat generation at the slit parts of unannealed Unicore wound cores, leading to inefficient cooling, even when immersed in oil or using air circulation.
Innovation Solution
A wound core design with a rectangular hollow portion and alternating planar and bent grain-oriented electrical steel sheets, where the surface roughness ratio of the L cross section is controlled between 1.5 and 12, allowing for increased surface area contact with oil or air, thereby enhancing cooling efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If grain-oriented electrical steel sheets are individually bent and stacked to form a wound core without annealing, then manufacturing complexity is reduced and production efficiency is improved, but heat generation at the slit parts increases causing temperature rise that is difficult to control
Solution Approach 1:
The invention shifts the cooling approach from internal/external fluid circulation to a surface-area-based radiative and conductive cooling mechanism by creating a three-dimensional rough surface structure through alternating planar and bent portions. This dimensional transformation allows heat dissipation through the expanded surface area without requiring complex cooling systems.
Solution Approach 2:
The invention creates local quality differences by forming alternating planar portions and bent portions with different surface characteristics along the steel sheets. The bent portions with smaller radius of curvature create protrusions that increase surface area and enhance local heat dissipation, while planar portions maintain structural integrity. This local variation in surface geometry optimizes overall cooling efficiency.
2Manufacturing precision
If conventional large-scale molding process is used to produce wound core, then shape precision is improved, but mechanical processing strain is applied to all steel sheets causing deterioration of iron loss and requiring strain relief annealing
Solution Approach 1:
The invention segments the bending operation into individual sheet-level actions rather than applying global molding pressure to all sheets simultaneously. Each steel sheet is bent independently with a small radius of curvature at specific corner portions, concentrating strain only where necessary for shape formation while leaving the majority of each sheet unstrained and maintaining its magnetic properties.
Solution Approach 2:
The invention applies local quality by concentrating bending strain only at the corner portions with small radius of curvature where shape definition is needed, while the planar portions and majority of each steel sheet remain free from mechanical processing strain. This localized strain approach preserves the magnetic properties of most of the steel sheet material.
3Temperature
If cooling ducts or oil immersion is used to control temperature, then cooling capability is improved, but device complexity and cost increase
Solution Approach 1:
The invention enables self-service cooling where the wound core's own geometry serves the cooling function. The alternating planar and bent portions create an intrinsic heat dissipation structure that operates without external cooling systems. The core structure itself provides the cooling capability through its expanded surface area, eliminating the need for separate cooling ducts, pumps, or oil circulation systems.
Solution Approach 2:
The invention extracts the cooling function from external cooling systems and integrates it directly into the core structure itself. By forming the cooling capability as an inherent geometric feature of the wound core through alternating planar and bent portions, the patent removes the need for separate cooling apparatus and simplifies the overall system.
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 design effectively reduces the temperature rise of iron cores and winding wires by improving cooling efficiency through increased surface area contact, while maintaining stable magnetic flux and minimizing iron loss.
Implementation Method 1
base steel is exposed to a slit part on an end surface of laminated steel sheets, and due to strain at the slit part, heat is generated at the end surface when the core is used to produce a transformer
Implementation Method 2
heat is generated at the end surface when the core is used to produce a transformer
Implementation Method 3
it is possible to increase a contact area with an oil or air, and thereby the cooling efficiency can increase
Implementation Method 4
contact area with an oil or air can increase, and thereby the cooling efficiency can increase
Data Source
AI summary
A wound core (10) in which, in a laminating direction, when the surface roughness of a steel sheet portion in a direction connecting a center in a sheet thickness direction of a grain-oriented electrical steel sheet (1) positioned on the innermost periphery of the wound core among the laminated grain-oriented electrical steel sheets (1) and a center in the sheet thickness direction of the grain-oriented electrical steel sheet (1) positioned on the outermost periphery of the wound core (10) is Ral, and the surface roughness of the grain-oriented electrical steel sheet (1) in a direction parallel to a longitudinal direction on an end surface of a planar portion (4) of the laminated grain-oriented electrical steel sheet (1) is Rac, a ratio Ral/Rac between Rat and Rac satisfies the relationship of 1.5≤Ral/Rac≤12.0.