Thermally Stable Rogowski Coil Core Design
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Solution Overview
Problem
Rogowski coils are sensitive to temperature changes due to their non-metallic cores with high and anisotropic coefficients of linear thermal expansion, leading to non-linearity in output measurements as the core expands or contracts.
Innovation Solution
A thermally stable Rogowski coil with a core having a coefficient of linear thermal expansion (CLTE) of less than 15 ppm/°C, made from materials like low CLTE liquid crystal polymer or ceramic, such as Steatite L-5, which maintains consistent dimensions across temperature variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a non-metallic core with high CLTE is used in the Rogowski coil, then the core can be easily manufactured and molded, but the output measurement becomes non-linear due to temperature-induced expansion and contraction
Solution Approach 1:
The patent changes the material parameter (CLTE) from high to low by selecting specific materials such as aluminum (CLTE < 25 ppm/°C), glass (CLTE < 10 ppm/°C), or ceramic (CLTE < 5 ppm/°C). This parameter change resolves the contradiction by maintaining dimensional stability across temperature variations, ensuring measurement linearity while still allowing for manufacturability through conventional molding processes.
2Manufacturing precision
If a plastic core with high CLTE is used, then the core can accommodate tight tolerances during manufacturing, but the coil configuration changes with temperature leading to output non-linearity
Solution Approach 1:
The patent changes the material parameter (CLTE) to a low value (< 25 ppm/°C) to maintain dimensional stability. This ensures that the core configuration remains consistent across temperature variations, preserving both the manufacturing precision achieved during winding and the operational stability during use.
Solution Approach 2:
The patent employs composite material solutions, such as glass-filled plastics or ceramic-aluminum composites, which combine the ease of molding from plastic with the dimensional stability of glass or ceramic. This composite approach resolves the contradiction by achieving both manufacturing precision and thermal stability.
3Reliability
If a low CLTE material is used for the core, then temperature stability is improved, but the manufacturing process becomes more complex
Solution Approach 1:
The patent selects materials with low CLTE (< 25 ppm/°C) such as aluminum, glass, or ceramic. While these materials may require different manufacturing approaches compared to standard plastics, the patent demonstrates that conventional molding and fabrication processes can still be applied, thus maintaining ease of manufacture while achieving superior temperature stability and reliability.
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 thermally stable core minimizes temperature-induced changes in the Rogowski coil's configuration, ensuring a stable output and reducing non-linearity in current measurements, thus enhancing the accuracy and reliability of current sensing.
Implementation Method 1
a plastic body has a high and anisotropic coefficient of linear thermal expansion (hereinafter, and as used herein, "CLTE"). That is, as the temperature changes, a plastic body with a high CLTE changes more than a body with a low CLTE
Implementation Method 2
A Rogowski coil is an electrical device generally used to measure alternating current (AC) or high-speed current pulses in another conductor
Data Source
Figure 1
AI summary
A Rogowski coil includes a thermally stable core with a toroid body and a winding including a conductive wire. The winding is disposed in a generally helical coil (36) about the core body.