Series-Arc Analysis Using a Normalized FFT Harmonic Energy Ratio in Power Distribution Systems With SFCL

초록

Detecting series arc faults in motor-connected distribution systems is challenging due to the dynamic impedance of induction motors. The inclusion of a Resistive Superconducting Fault Current Limiter (SFCL) further complicates detection by potentially dampening the high-frequency arc signatures required for identification. This paper experimentally investigates whether a harmonic-based detection metric remains robust under the combined influence of motor inrush dynamics and SFCL resistive operation We utilize a three-cycle sliding Fast Fourier Transform (FFT) to compute a band-limited harmonic energy ratio, H(k) over the 200-2000 Hz band. Tests compare wye and delta starting methods and two arc locations: the main feeder (Case 1) and the motor branch (Case 2). Experimental results show that under the same line voltage, the delta connection produced a larger natural inrush(approximate to 65A) compared to the wye connection (approximate to 26A). The SFCL effectively functioned as a soft-starter, limiting the delta inrush to 35 A via a resistive quench(approximate to 80V). Although this resistive damping attenuated the absolute arc current spectra, the normalized metric H(k) successfully distinguished arc faults. In Case 1, H(k) consistently exceeded the baseline by a factor of 3 to 8. In Case 2, despite a masking effect caused by the parallel resistive load under wye starting, the metric remained reliable, showing a distinct 5-fold increase in the delta configuration and a gradual rise at the motor terminals. This study validates that the proposed harmonic-energy metric provides a practical, connection-aware indicator for series arc detection, capable of overcoming the signal suppression introduced by the SFCL.

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