A Frequency-Based Impedance Differential Protection Scheme for Undersea Observation Networks

Electric energy is the lifeblood of the operation of the undersea observation network. The operation of the undersea observation network and observation equipment is inseparable from electric energy. The undersea observation network studied in this paper is a single-stage constant voltage DC power supply mode, which uses a single-core copper wire of a photoelectric composite cable and seawater as a power transmission circuit. In order to clear faults efficiently, this paper proposes a frequency-based impedance differential protection scheme. The electrochemical process of electrode-seawater circuit is studied, the characteristics of submarine cable electrode seawater power supply parameters and frequency variation mechanism are revealed respectively. This paper establishes the broadband RC impedance model of the anode-seawater-cathode circuit. Based on the broadband impedance spectroscopy, an impedance differential protection scheme is proposed. The voltage and current of the branch unit are converted into impedance signals and expanded in the frequency domain, and appropriate frequency value is selected to design a differential protection criterion. The validity of the impedance differential protection scheme is proved by simulations in PSCAD/EMTDC. The scheme offers a theoretical basis and technical support for the safe, reliable, high-quality, and stable operation of deep sea facilities.