The power supply system is fundamental to the safe and reliable operation of undersea observation networks. Due to the low observability and accessibility of undersea observation networks

combined with the unique power supply structure involving seawater and electrodes in a monopolar power supply loop

submarine cable fault localization becomes particularly complex. This paper focuses on the critical challenge of submarine cable fault localization. To address the deficiencies in existing impedance modeling of power supply loops in undersea observation networks

this paper develops a frequency-variable impedance model for the seawater- electrode-cable loop through π-type equivalent modeling of submarine cables combined with electrochemical analysis of the seawater-electrode interface. By modeling the impedance network of the post-fault seawater-electrode-cable loop

the input impedance is obtained. This method relies solely on electrical data collected from shore stations to derive a complete and accurate frequency-variable input impedance spectrum of the power supply loop. Consequently

a novel method for submarine cable fault localization based on frequency-dependent impedance characteristics is proposed. This method generates a localization function through frequency sweeping

correlating fault distance with impedance

thereby achieving precise fault distance calculation. The research results indicate that this method attains high precision in submarine cable fault localization and exhibits good robustness against varying fault locations and transition resistances

marking a significant advancement in this field. This breakthrough enhances the protective capabilities and fault localization accuracy for the power supply system in undersea observation networks and promotes the application of cathodic DC technology in various marine development and engineering projects.