Research On Controllable Branching Unit In Observatory Network

The observatory network is always located on the seafloor, which makes it very difficult to access after the installation. For the long-term monitoring purpose, the power delivery system of the observatory network must be highly reliable. The system shall be maintenance free without regular replacement of any components. On the other hand, for the complicated environment undersea and network itself, various unpredictable cable faults can happen. For the system reliability to keep the network running, the advantages of branching units outstands.The purpose of power system protection is to remove the fault parts of the network, so the remaining cables will not be affected. Here I propose an approach to adopt a protective relaying scheme to separate the faulted parts from the whole system. This scheme requires a branching unit connected between the backbone cable and spur cable, with switching device and controller, the power of the controller is tapped from the backbone. The current observatory network is working in a -10KV high voltage DC circuit, direct switching demand highly for the switching devices, so in this paper, we adopt a relative lower voltage and lower current power supply mode to avoid directly breaking. There are different topologies of power system. For the existing tree topology network, the analogical BU is adopted with a T-shaped switching device. Different shore voltage level is used to control the switching device. For the future double shore topology, a digital BU is designed. With a triangle-shape switching device, the shore power supply is programmed to be received by MSP430, therefore to control the switching device.With Pspice simulation and cable connecting test conducted in the lab, the control function of analogical BU from different voltage is verified. And there is no interruption between different control voltages. For the digital BU test, the results show that MSP430 can sample the correct programmed signal and therefor control the switching device accurately. Also, the tests prove that the working current running on the backbone cable of the two BUs are always between 10 mA and 20 mA, as the resistance of the cable is 1Ω/km, the voltage cost on per 100 km is about 1-2 V, so this can be the reference for control voltage setting of the two Bus to avoid voltage insufficient for the controlling.