Abstract:Cabled seafloor observatory networks (CSONs) can provide a large amount of undersea scientific instruments with sustained and abundant power. According to the principles of reliability and economy, the paper illustrates why the power system of CSONs is suitable to adopt the negative monopole DC transmission scheme with the seawater as the current returning path by parallel connecting undersea loads, and employing the cascaded high frequency DC DC conversion system, and then the CSONs’ physical structure is established based on the analysis. According to the CSON’s characteristics, several typical undersea power system topologies are summarized. With the average power feeding reliability of the undersea stations as the reliability index, the reliability indexes of these typical topologies are calculated and compared. This method can provide a basis for the CSONs’ topology planning. Furthermore, the operation mode of the undersea power system is designed to enhance the CSONs’ fault tolerance capability. The study can be a reference for the future construction of large scale national CSONs.