Cushioning Material for Resin Cast Transformer Core
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Solution Overview
Problem
Thermoset resin used in transformer core-coil assemblies shrinks during curing, causing mechanical stresses and strains that distort the magnetic core, increase core loss, and reduce transformer sensitivity, with existing solutions like molded boots or cups being expensive and ineffective for varying core sizes.
Innovation Solution
A cushioning material comprising a force absorption layer of polymeric foam and a force distribution layer of cellulosic material, such as pressboard, is applied around the transformer core to absorb and distribute the stresses from the shrinking resin, preventing distortion and cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If thermoset resin is used to encapsulate the core-coil assembly, then electrical and mechanical protection is provided, but the resin shrinks during curing causing mechanical stresses and strains that distort the magnetic core
Solution Approach 1:
A cushioning material is placed between the magnetic core and the thermoset resin before encapsulation. This cushioning material absorbs the mechanical stresses and strains generated during resin curing, preventing direct transmission of forces to the core and thereby preventing core distortion while maintaining protective encapsulation.
Solution Approach 2:
The cushioning material serves as an intermediary layer between the magnetic core and the shrinking thermoset resin. It mediates the interaction by absorbing expansion and shrinkage forces, preventing direct contact between the resin and core, thus eliminating the harmful mechanical stresses while preserving the protective function.
2Reliability
If molded boots or cups are used to protect the core, then core protection is provided, but each core requires a uniquely molded component increasing cost
Solution Approach 1:
The cushioning material is designed with universal dimensions and properties that can accommodate various core sizes and shapes. Unlike custom-molded boots or cups requiring separate tooling for each core variant, this standardized cushioning material provides effective protection across different transformer configurations, significantly reducing manufacturing cost and complexity.
Solution Approach 2:
The cushioning material's physical parameters (such as compressibility, density, and thickness) are optimized to provide effective protection without requiring custom molding. By adjusting these parameters within a standardized design, the same cushioning material can effectively protect cores of varying sizes, eliminating the need for multiple custom-molded components.
3Duration of action of stationary object
If thermoset resin shrinks around sharp protrusions, then encapsulation is completed, but cracks form in the resin compromising the seal
Solution Approach 1:
The cushioning material is positioned beforehand at locations where sharp protrusions may cause resin cracking during shrinkage. It absorbs the concentrated stresses at these critical points, preventing crack initiation and propagation, thereby maintaining seal integrity while completing the encapsulation process.
Solution Approach 2:
The cushioning material acts as an intermediary that prevents direct contact between the shrinking resin and sharp protrusions on the core or coil assembly. By distributing the shrinkage forces and eliminating stress concentration points, it prevents resin cracking and maintains the integrity of the encapsulating seal.
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
The cushioning material effectively reduces mechanical stresses on the transformer core, maintains magnetic flux integrity, and prevents resin cracking, improving transformer accuracy and sensitivity while being cost-effective for various core sizes.
Implementation Method 1
a force absorption layer comprising a polymeric foam... The cushioning material effectively reduces mechanical stresses on the transformer core
Implementation Method 2
a force distribution layer comprising a cellulosic material, such as pressboard... The force distribution layer is harder than the force absorption layer
Implementation Method 3
The encapsulating resin is typically a thermoset polymer or resin, which is a polymer material that cures, through the addition of energy, to a stronger form. The energy may be in the form of heat (generally above 200 degrees Celsius), through a chemical reaction
Implementation Method 4
When a thermoset resin cures, molecules in the resin cross-link, which causes the resin to harden
Implementation Method 5
When a thermoset resin cures, the resin typically shrinks. Because the resin surrounds the core, the shrinking thermoset resin exerts high mechanical stresses and strains on the grain oriented silicon steel core
Data Source
AI summary
A resin cast transformer having a core covered by a cushioning material is provided. The cushioning material is in contact with the core and includes a force absorption layer adjoining a force distribution layer. The force distribution layer is harder than the force absorption layer.