Characterization of short-circuit faults in energized conductors under varying thermal radiation intensities

To elucidate the evolution patterns and hazard characteristics of overheating-induced short-circuit faults in energized conductors under external thermal radiation, this study systematically investigated critical heat flux, characteristic temperatures, fault initiation time, insulation resistance evolution, short-circuit current-voltage waveform characteristics, and arc energy variation. The objective was to identify key parameters for the early warning of electrical fires during conductor short-circuit failure under varying thermal radiation intensities. The findings aim to provide experimental evidence for risk identification and assessment of electrical circuit failures in high-temperature environments.

Using an electrical fault simulation apparatus, stable thermal radiation intensities of 23—32kW·m^-2 were applied to ZR-RVVB conductors operating under rated current conditions. Parameters including surface and internal temperatures, insulation resistance, pre-and post-short-circuit current and voltage waveforms, and fault occurrence times were recorded simultaneously. Thermal failure stages were defined using temperature-time curves. Short-circuit types were classified through waveform and time-frequency domain analyses, and short-circuit arc energy was calculated based on voltage-current integration. Comparative analyses were conducted to determine parameter variation patterns across different thermal radiation intensities.

Experimental findings indicated that 23kW·m^-2 represents the minimum critical thermal radiation intensity that causes short-circuit failures in ZR-RVVB conductors under rated current conditions. With increasing thermal radiation intensity, the conductor temperature rise showed four stages: transient thermal shock, accelerated pyrolysis, critical failure, and thermal steady state. The initial pyrolysis temperature (T₁), peak temperature (T₂), short-circuit trigger temperature (T_sc), and steady-state temperature (T₃) increased approximately linearly with increasing heat flux. Meanwhile, the duration of each stage decreased with increasing heat flux, showing a power-law relationship. This reduction is associated with faster heating and accelerated insulation degradation under higher thermal radiation intensities. Notably, the short-circuit trigger time shortened from ~1053.4s to 172.4s. At a heat flux of 32kW·m^-2, the insulation resistance dropped rapidly to ~0GΩ within 180s. Overall, insulation resistance declined significantly with increasing thermal radiation intensity. A reduction below ~1GΩ signaled imminent insulation failure. Fault mechanisms transitioned from metallic short circuits to carbonization path-type and arc-type faults as the thermal radiation intensity increased. At a heat flux of 25kW·m^-2, metallic short circuits were the dominant failure mode, accounting for ~70% of failures. When the heat flux exceeded 26kW·m^-2, the frequency of carbonization path-type faults increased significantly, peaking near 31kW·m^-2. Time-frequency energy analysis indicated that arc-type short circuits exhibited the highest high-frequency energy characteristic parameters, with a high-frequency energy peak (HHF) of 0.860 and a high-frequency energy ratio (RHF) of 0.416, both of which were significantly higher than those of the other two fault types. Energy released after short-circuit increased significantly with increasing thermal radiation intensity; arc-type faults released the highest energy (approximately ~9324.89J), followed by carbonization path-type faults. Meanwhile, metallic short circuits released the least energy. This indicated that higher thermal radiation intensities lead to greater short-circuit energy release and increased destructive potential.

This study characterized the temperature rise behavior, insulation resistance evolution, fault type transitions, and energy release characteristics of energized conductors under varying thermal radiation intensities. The findings provide a foundation for rapid short-circuit fault classification and the development of early-warning models.