Permanent Magnet Ring Core Fault Current Limiter
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Solution Overview
Problem
Existing fault current limiters, such as Saturated Iron Core FCLs and Superconducting FCLs, are not suitable for smaller power operations due to high costs, large mass, high cooling requirements, and thermal instabilities, and they are not desirable for circuits with power electronics devices like transistors and diodes.
Innovation Solution
A fault current limiter with a ring-shaped core structure comprising a first and second magnetisable ring-shaped core member, an AC magnetomotive force source, and permanent magnets positioned to bridge the gap between the core members, providing a closed magnetic circuit that limits fault currents without the need for superconducting systems or electromagnets, and allowing for automatic reset after a fault event.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Saturated Iron Core FCL or Superconducting FCL is used, then fault current limiting capability is improved, but cost, mass, and complexity increase significantly
Solution Approach 1:
The patent replaces expensive superconducting materials and complex iron core systems with permanent magnets that provide the necessary magnetic field. The permanent magnets are a simple, cost-effective alternative that eliminates the need for costly cooling mechanisms and complex control systems while maintaining fault current limiting capability
Solution Approach 2:
The patent extracts the essential function (providing a magnetic field for core saturation) from the complex superconducting or iron core systems and implements it using only permanent magnets. This removes the unnecessary complexity of superconducting coils, cooling systems, or large iron cores while retaining the core functionality
2Reliability
If Saturated Iron Core FCL is used, then fault current limiting capability is improved, but device mass and volume increase
Solution Approach 1:
The patent uses permanent magnets instead of large iron cores or superconducting materials, dramatically reducing device mass. The permanent magnets provide sufficient magnetic field strength without requiring the bulky infrastructure of traditional FCL designs
Solution Approach 2:
The patent changes the magnetic field generation approach from requiring large amounts of material (iron cores or superconducting coils) to using concentrated permanent magnets. This parameter change in magnetic field source enables compact, lightweight design while maintaining effectiveness
3Reliability
If Superconducting FCL is used, then fault current limiting capability is improved, but cooling requirements and operational complexity increase
Solution Approach 1:
The patent replaces superconducting materials requiring cryogenic cooling with permanent magnets that operate at ambient temperature. This eliminates the need for expensive cooling systems and complex temperature control while maintaining fault current limiting functionality
Solution Approach 2:
The patent substitutes the mechanical/thermal system of superconducting cooling with a static magnetic field system using permanent magnets. This replaces the complex thermal management infrastructure with a simple, passive magnetic field source
4Reliability
If permanent magnets are positioned to bridge the gap between core members, then magnetic circuit efficiency is improved, but risk of demagnetization increases
Solution Approach 1:
The patent divides the magnetic circuit into discrete segments with permanent magnets positioned at specific locations (bridging gaps between core members). This segmentation allows the magnetic field to be distributed effectively while protecting individual magnets from excessive stress that could cause demagnetization
Solution Approach 2:
The patent positions permanent magnets at specific locations where they bridge gaps between core members, creating localized regions of high magnetic field strength. This local concentration of magnetic quality improves overall circuit efficiency while the distributed positioning prevents any single magnet from experiencing demagnetizing conditions
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 effectively limits fault currents while minimizing material costs and avoiding demagnetization of permanent magnets, enabling efficient operation in both low and high power systems, including those with power electronics, by distributing DC flux and maintaining core saturation without significant AC reluctance increase.
Implementation Method 1
The permanent magnet causes the core to saturate in the normal operating state
Implementation Method 2
The permanent magnets are positioned to provide a magnetic circuit within at least part of the magnetisable core members
Implementation Method 3
an AC magnetomotive force source configured to generate a varying magnetic flux in at least a portion of the first and second magnetisable core members, wherein the AC magnetomotive force source is an AC coil
Implementation Method 4
generate a varying magnetic flux in at least a portion of the first and second magnetisable core members
Implementation Method 5
During a fault condition a large AC current value (the fault current) forces each of the cores of the device to come out of saturation in alternative half-cycles. The mostly unsaturated first core in combination with the mostly saturated second core (and vice versa) restricts the flow of the fault current since the inductance of the coil is caused to increase
Data Source
Figure 1
Figure 2A~2B
Figure 3~4A
AI summary
A fault current limiter (FCL) has a core structure with a first and second magnetisable core members and an AC magnetomotive force source configured to generate a varying magnetic flux in at least a portion of the first and second magnetisable core members. Static magnetomotive force sources being positioned to provide a magnetic circuit within at least part of the magnetisable core members. The FCL may have a ring core structure and the static magnetomotive force sources may include a mitred or tapered joint interface with the core member.