Grain-Oriented Electrical Steel Coating for Low Interlaminar Current
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Solution Overview
Problem
Grain oriented electrical steel sheets used in transformers often exhibit insufficient insulation properties when stacked and processed into cores, leading to leakage currents or partial discharge due to inadequate interlaminar insulation resistance, which is not detected during standard pre-shipment inspections.
Innovation Solution
A grain oriented electrical steel sheet with a coating on both surfaces, having specific hardness and surface roughness, and produced using a coating liquid with controlled molar ratios of metal elements and silica, is subjected to a rubbing test to ensure an interlaminar current value of not more than 0.10 A under defined conditions, ensuring excellent insulation properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a coating is formed on the steel sheet to provide insulation property, then the insulation property is improved, but the coating may become too hard causing damage during stacking and processing
Solution Approach 1:
The patent changes the chemical composition parameters of the coating by controlling the molar ratios of metal elements (M1, M2) to silica in the coating liquid. Specifically, M1/S ≥ 0.15, M2/S ≤ 0.15, and P/S ≥ 0.20, which produces a coating with appropriate hardness that balances insulation properties with resistance to damage during processing.
Solution Approach 2:
The patent uses a composite coating material consisting of multiple metal elements (M1 and M2) combined with silica and phosphoric acid components. This composite structure allows the coating to achieve both sufficient insulation properties and appropriate mechanical strength to withstand stacking and processing without being too hard or too soft.
2Reliability
If the coating is formed with high metal element content to improve insulation, then the insulation property is improved, but the coating hardness increases causing interlaminar current
Solution Approach 1:
The patent precisely controls the molar ratio parameters of metal elements to silica (M1/S ≥ 0.15, M2/S ≤ 0.15) and phosphoric acid to silica (P/S ≥ 0.20). This parameter optimization ensures the coating achieves adequate insulation properties while maintaining appropriate hardness to prevent interlaminar current, resolving the contradiction between insulation performance and harmful electrical effects.
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 solution provides a grain oriented electrical steel sheet with enhanced insulation properties, preventing leakage currents and partial discharge in transformers, even under severe processing conditions, by accurately evaluating insulation quality through the rubbing test.
Implementation Method 1
an insulating coating formed by baking a coating liquid containing phosphate, colloidal silica, and chromic anhydride
Implementation Method 2
the insulating coating formed at high temperature followed by cooling applies tension to a steel sheet owing to the difference in thermal expansion coefficient from that of the steel sheet
Implementation Method 3
the insulating coating formed at high temperature followed by cooling applies tension to a steel sheet owing to the difference in thermal expansion coefficient
Data Source
AI summary
A grain oriented electrical steel sheet has excellent insulation property and includes: a steel sheet; and a coating disposed on each of both surfaces of the steel sheet, wherein an interlaminar current value after a rubbing test is not more than 0.10 A, the rubbing test being conducted by stacking two sheets of the grain oriented electrical steel sheet and rubbing the two sheets against each other to make 90 reciprocations under conditions of a surface pressure of 200 Pa, a rubbing speed of 0.10 m/s, and a reciprocating stroke of 50 mm.