Design and implementation of an adaptive protection strategy for a 0.4 kV safe anti-electric-shock maintenance power supply box in smart grids

Ensuring personnel safety and operational reliability in 0.4 kV (kilovolt) distribution networks during maintenance remains a critical challenge, especially under diverse environmental and load conditions. Traditional fixed-threshold protection schemes often fail to adapt to dynamic fault signals caused by varying earth impedance, moisture, and nonlinear loads, resulting in false alarms or missed detections. To address these limitations, this paper proposes an adaptive protection strategy for 0.4 kV maintenance environments, combining harmonic distortion rate and transient waveform slope as detection criteria. An experimental platform was constructed, featuring a 10/0.4 kV transformer, dual-feeder topology, configurable loads, adjustable fault resistances, and arc generators to emulate realistic fault scenarios. Multi-point measurements of voltages, currents, and residual currents were conducted under varying conductor cross-sectional areas, fault locations, contact areas, and humidity levels. Results show that the proposed method accurately detects earth faults and electric shock events with higher sensitivity and specificity than conventional fixed-threshold methods, even under adverse conditions. The strategy effectively mitigates the impact of load switching and environmental noise, improving protection reliability.