Abstract: In order to solve the problem of difficult to accurately locate single-phase grounding faults in small current grounding systems of chemical plants, this paper studies the mechanism, type characteristics, and system hazards of fault generation, and analyzes the limitations of traditional detection methods such as slow response, poor anti-interference ability, and low recognition accuracy under small current conditions. Based on this, a small current line selection device that integrates zero sequence current surge extraction, phase consistency matching, and wavelet transform analysis is constructed. Through system composition modeling and algorithm formula design, a fault recognition technology path with high response speed and high adaptability is proposed, and deployed in the actual power distribution system of a chemical plant. Through typical feeder layout and fault data acquisition, the device's real-time recognition ability and stable operation performance are verified at low current levels. The analysis results show that the line selection device has high accuracy and low response delay in complex working conditions, which can effectively meet the engineering requirements of real-time and reliable grounding fault location in the chemical industry, and has good engineering application and promotion.