Biased Magnetic Core Circuit for DC Current Rise Limiting
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Solution Overview
Problem
In DC grids, high currents during switch-off operations lead to intense switching arcs, which existing technologies struggle to mitigate effectively due to magnetic core saturation and limited current limiting capabilities, especially in applications with limited space and slow switching devices.
Innovation Solution
A device comprising a first magnetic core with an annular path, a permanent magnet arrangement, and a coil, where the magnetic core is biased by the magnet to extend its usable range before saturation, and a bypass air gap to protect against demagnetization, allowing for effective current limiting and overcurrent protection in a compact design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a magnetic core is used to limit current rise, then the current limiting effect is improved, but the magnetic core becomes saturated by DC voltage which reduces its effectiveness
Solution Approach 1:
The patent introduces an auxiliary magnetic circuit with permanent magnets as an intermediary system. This auxiliary circuit generates a bias magnetic field that opposes the saturation-causing flux, thereby preventing the main magnetic core from saturating under DC voltage conditions and maintaining its current limiting capability.
Solution Approach 2:
The patent changes the magnetic field parameters by introducing a bias magnetic field through permanent magnets. This bias field modifies the operating point of the magnetic core, shifting it to a region where the core does not saturate under DC voltage, thus maintaining inductance and current limiting effectiveness.
2Reliability
If permanent magnets are used to bias the magnetic core, then the usable range before saturation is enlarged, but very high currents can demagnetize the permanent magnet
Solution Approach 1:
The patent introduces a bypass air gap as an intermediary element in the magnetic circuit. This air gap provides an alternative path for magnetic flux, reducing the flux density through the permanent magnet during high current events and preventing demagnetization while maintaining the bias field's current limiting effectiveness.
Solution Approach 2:
The bypass air gap acts as a protective cushion for the permanent magnet. By providing a low-reluctance alternative path for magnetic flux before the magnet can be exposed to damaging flux densities, it preemptively protects the magnet from demagnetization during overcurrent events.
3Stability of the object's composition
If air coils are used instead of magnetic cores, then saturation problems are avoided, but the device becomes very large and unusable in many applications
Solution Approach 1:
The patent creates a composite magnetic circuit system combining a magnetic core, permanent magnets, and a bypass air gap. This composite structure maintains the space-saving advantages of magnetic cores while incorporating elements that prevent saturation and protect against demagnetization, achieving both compact size and operational stability.
Solution Approach 2:
The magnetic circuit is segmented into multiple functional parts: the main magnetic core for current limiting, the auxiliary magnetic circuit with permanent magnets for biasing, and the bypass air gap for protection. This segmentation allows each component to perform its specific function optimally while maintaining a compact overall structure.
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 reduces current rise during short circuits or arc flashes, preventing switching contact deterioration and ensuring reliable operation in DC grids, even in applications with limited space, by maintaining inductance over a wide current range and preventing demagnetization of the permanent magnet.
Implementation Method 1
permanent magnets have been proposed which generate a magnetic field in opposite direction of the magnetic field caused by a current
Implementation Method 2
the magnetic core of the inductances tends to be saturated by the DC voltage what limits the effect of reducing the current rise
Implementation Method 3
a first coil being wound around the first magnetic core
Implementation Method 4
a first magnetic core with at least one annular path for a magnetic flux
Implementation Method 5
a first sub path of the sub paths comprises a first bypass air gap
Data Source
AI summary
A device for limiting or reducing a current rise is disclosed, which comprises a first magnetic core with at least one annular path for a magnetic flux, a first magnet arrangement having at least one permanent magnet in the at least one annular path of the first magnetic core and a first coil being wound around the first magnetic core. The at least one annular path has a first section with parallel sub paths, wherein a first sub path of the sub paths comprises a first bypass air gap and a second sub path of the sub paths is a continuous path comprising said first magnet arrangement. Further on, an arrangement with such a device and an electric circuit with such an arrangement is disclosed.