Electrical Characteristics of Low-Voltage AC Series Arcs According to Load Current Under Linear Load Conditions

The electrical characteristics of low-voltage AC series arcs according to the load current (1, 3, and 5 A) were investigated under linear load conditions. A current waveform analysis identified nonlinear distortion, particularly the shoulder effect near zero-crossing regions. Frequency domain analyses using fast Fourier transform and total harmonic distortion (THD) demonstrated that harmonic current components are primarily concentrated in the low-frequency range below 3 kHz, where cumulative THD values saturate. As the load current increased, the THD delta between normal and arc conditions expanded from 1.526% to 2.084%, reflecting intensified nonlinearity. A detailed harmonic analysis revealed that the ninth harmonic maintains a consistent level deviation of approximately 15 dB, regardless of the current magnitude, serving as a robust indicator. Furthermore, the odd/even harmonic root mean square current ratio increased by up to 153.3% at 5 A, exhibiting a distinct feature for arc discrimination. This phenomenon is driven by the enhanced generation of odd harmonics and the sustained suppression of even harmonics owing to half-wave symmetry. In this research, the harmonic characteristics were quantified based on the load current, and the critical factors for effective arc fault discrimination in linear load environments were identified.