Distance Estimation for Early Three-core Cable Fault based on Multiple Amplitude Ratios Fusion of Grounding Line Current Selected Frequency Band

Early cable faults are increasingly common in urban distribution networks. This paper analyzes the mechanism of grounding line current signal generation and propagation in cables with early faults, revealing the intrinsic relationship between each frequency component's amplitude and fault location. Based on this analysis, a distance estimation method for early faults in three-core cables is proposed using multiple amplitude ratios fusion within selected frequency band. This approach effectively reduces reliance on accurate extraction of single-frequency component’s amplitude and is suitable for sub-cycle early faults. Theoretical research and example analysis results demonstrate that this method exhibits high fault distance estimation accuracy while being less susceptible to variations in fault conditions.