Protection Scheme for Subsea Observatory Power Supply System Based on Control and Protection Coordination
Chu Xu1, Liu Qi1, Lü Haoze1, Yan Yabing2, Xu Liqiang2
1. National Electric Power Conversion and Control Engineering Technology Research Center Hunan University Changsha 410082 China; 2. Electric Power Research Institute of State Grid Hunan Electric Power Co. Ltd Changsha 410007 China
Abstract The power supply system of submarine observation network with cable provides energy supply for submarine observation equipment, communication equipment and control and protection equipment, and its security and stability are directly related to the continuous and reliable operation of the whole submarine observation network. Among them, the constant voltage power supply system of the seabed observation network has the advantages of strong expansion ability and high energy conversion efficiency, which has been adopted by many subsea observation networks already in operation or under construction. Some submarine cable fault detection methods based on photoelectric technology and traveling wave analysis have been proposed, but there are some problems such as too long detection time and difficult implementation. To address these issues, this paper proposes a protection for subsea observatory power supply system based on control and protection coordination, which can limit the rapid spread of fault current, and accurately identify and reliably isolate fault optic-electric composite submarine cable. Firstly, the overall structure of the constant voltage subsea observatory network is introduced, and the operating mode and control characteristics of shore converter, branch unit, connection box and photoelectric composite cable are analyzed in detail. Then, the active control of shore stations is proposed to limit the output current during faults. Then, the fault identification criterion of branch cable and fault location criterion of backbone cable based on branch unit current polarity are proposed. The inverse time low voltage protection based on the instantaneous voltage of branch unit and shore station is constructed to determine the switch position to be switched. Finally, the protection outlet to switch can realize the rapid action of branch unit or shore station break switch under limited current level, and achieve effective fault isolation. The simulation model of the power supply system of the negative constant voltage submarine observation network is built on the PSCAD/EMTDC electromagnetic simulation platform, which verifies the feasibility and effectiveness of the proposed protection strategy of the power supply system of the submarine observation network. Simulation results on the waveforms in various fault scenarios show that in the fault scenario, if the current limiting control is not put into operation, the DC side voltage will drop to zero quickly in a short time, the amplitude of the DC side current will increase rapidly, and fault current will reach the normal operating value -7.2 A dozen times. If the fault is timely put into current limiting control, the amplitude of the DC side voltage will gradually decrease and stabilize at -8 kV, the DC side current will stabilize at -9.3 A, and the peak value of the current only fluctuates to about twice the rated current during the control adjustment process. When the branch cable fails, the switch connected to the branch cable in the branch unit can reliably act to remove the fault, and other switches do not malfunction. When the main cable fails, the fault section can be accurately identified, and the branch unit switches on both sides of the fault point can be effectively disconnected. The protection can achieve a fault response of up to 20 Ω transition resistance in about 50 ms, and the protection performance will not deteriorate under severe noise interference with SNR=30 dB. The following conclusions can be drawn from the simulation analysis: (1) The proposed protection covers the whole section of the submarine cable without relying on communication, and the selective discrimination and isolation of submarine cable faults can be realized only by local measurement of shore station and branch unit. (2) The proposed protection has high tolerance to transition resistance, and has the ability to cope with interference of noise. (3) The protection criterion and shore power supply current limiting control are coordinated to realize the cooperation of control and protection, which can effectively suppress the fault current and realize the rapid fault identification and isolation.
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2023, Vol. 38 
