Magnetothermal Current Limiter for Low Voltage Applications
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Solution Overview
Problem
Existing current limiter devices for low voltage electrical installations require cryogenic environments, are costly, and alter line impedance under nominal conditions, making them unsuitable for low voltage applications.
Innovation Solution
An inductive current limiting device using a magnetothermal material, such as a NiCoMnX alloy, which changes magnetization with temperature, allowing for current limiting without cryogenic means and maintaining nominal impedance, featuring a magnetic circuit with a torus shape and coiled copper wire, and adjustable resistance based on network voltage and desired limited current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If superconducting materials are used in current limiting devices, then current limiting capability is improved, but cryogenic infrastructure is required increasing device complexity and cost
Solution Approach 1:
The patent changes the operating temperature parameter from cryogenic (superconducting) conditions to ambient temperature by using magnetothermal materials. The material's magnetization parameter changes with temperature, allowing current limiting functionality without requiring cryogenic infrastructure.
Solution Approach 2:
The patent replaces expensive superconducting materials requiring complex cryogenic systems with cheaper magnetothermal materials that operate at ambient temperature. This substitution eliminates the need for costly cryogenic infrastructure while maintaining current limiting capability.
2Reliability
If high impedance is inserted to limit current, then current limiting is achieved, but line characteristics are modified under normal operation
Solution Approach 1:
The patent uses a dynamic magnetic circuit whose permeability changes with temperature. Under normal operating conditions, the magnetic circuit maintains low impedance allowing normal line characteristics. When fault current causes temperature rise, the magnetothermal material's magnetization changes, increasing impedance to limit fault current dynamically.
Solution Approach 2:
The patent changes the magnetic permeability parameter of the circuit based on temperature. At normal temperatures, permeability remains stable maintaining normal impedance. At elevated temperatures from fault conditions, permeability changes to increase impedance and limit current, thus avoiding permanent modification of line characteristics.
3Reliability
If inductive current limiting devices with superconductors are used, then current limiting is improved, but operating cost and maintenance requirements increase
Solution Approach 1:
The patent employs a self-regulating system where the fault current itself heats the magnetothermal material, which then automatically increases magnetization and limits the current. This passive response eliminates the need for external control systems, cooling infrastructure, and associated maintenance, reducing operating costs.
Solution Approach 2:
The patent replaces expensive superconducting materials requiring ongoing cryogenic maintenance with inexpensive magnetothermal materials operating at ambient temperature. This eliminates continuous operating costs for cooling and reduces maintenance requirements significantly.
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
Effectively limits currents at ambient temperature without cryogenic requirements, maintaining normal impedance and reducing operational costs, making it suitable for low voltage applications.
Implementation Method 1
the magnetic circuit comprises a magnetothermal (or magnetocaloric) material, i.e. a material for which the magnetization increases with temperature above a first temperature greater than or equal to 330 K, and notably exhibits a peak, the maximum of which is greater than 40 emu/g
Implementation Method 2
Each of the primary and secondary can comprise coiling, notably of copper wire, around the magnetic circuit
Data Source
AI summary
A current limiting device including a transformer including an element made from a magnetothermal material, a primary conductor, and a secondary winding. Heat is generated by the current flowing through the primary conductor and when the current exceeds a certain threshold it modifies the coupling coefficient of the transformer, which makes it possible to limit the current in the primary conductor.