Novel core technologies for highly compact fault current limiters

Manley, James 2025. Novel core technologies for highly compact fault current limiters. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

This thesis presents the development and validation of a novel passive fault current limiter (FCL) based on a single magnetic core constructed from grain oriented electrical steel (GOES) subjected to high compressive stress. Unlike conventional saturated core FCLs, which require permanent magnets or DC windings to maintain a low-impedance state during normal operation, the proposed design passively achieves the required impedance modulation through the combined effects of magnetic anisotropy and magnetoelastic stress. Magnetic characterization of GOES laminations cut transverse to the rolling direction (TD) demonstrated that applying compressive stress up to 100MPa significantly altered the B–H characteristics. Under such stress, the initial relative permeability dropped to approximately 250, enabling the device to operate in a low-impedance regime under nominal conditions. At higher magnetic fields corresponding to fault events, permeability increased beyond 1000, resulting in rapid impedance rise and effective current limiting. The magnetic behaviour was integrated into both MATLAB Simulink and MagNet finite element models to evaluate FCL performance under dynamic fault conditions. Simulations of a 10kV system showed peak current reductions of up to 33% under fault conditions, while maintaining minimal impact on normal load current. A prototype FCL core was constructed using stacked laminations, and experimental B–H measurements confirmed the scalability and consistency of magnetic response across a range of compressive stresses. This approach eliminates the need for external excitation, reduces core material volume by approximately 50% compared to dual-core designs, and offers a compact, low-cost solution suitable for low- to medium-voltage grid applications. While mechanical challenges remain—particularly in applying and maintaining uniform compressive stress at scale—the results strongly support the viability of this method as a foundation for next-generation passive FCL technologies.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Engineering
Uncontrolled Keywords:	1. Fault Current Limiter 2. Compressive stress 3. Grain oriented electrical steel 4. Non-linear inductance 5. Transverse direction
Funders:	EPSRC
Date of First Compliant Deposit:	31 March 2026
Last Modified:	01 Apr 2026 09:00
URI:	https://orca.cardiff.ac.uk/id/eprint/185701

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