Protection of Multi-Terminal Hybrid Transmission Lines Based on Dynamic States Estimation

Multi-terminal hybrid transmission lines including overhead lines and cables are adopted to connect off-shore wind farms to the power grid. This paper proposes a protection method for multi-terminal hybrid lines through dynamic states estimation. The method accurately considers the shunt capacitance through the overhead line and cable. Firstly, the dynamic model of the multi-terminal hybrid line is established, where the distributed parameter lines are modeled by multiple $\pi$ sections. All the physical laws are listed through differential and algebraic equations (DAEs) in matrix forms. Secondly, the principle of dynamic states estimation (DSE) is presented to quantify the consistency between the healthy line dynamic model and the available measurements at all terminals of the line, and the protection logic is designed. Numerical experiments of an example test system show the operation speed, dependability and security of the DSE based line protection.