A New Pilot Protection Based on Tellegen’s Theorem for Receiving-end AC Transmission Lines of LCC-HVDC Hybrid System

LCC-HVDC technology holds a significant proportion in China's direct current transmission projects. When a fault occurs on the receiving-end AC system, leading to the commutation failure, the receiving AC system's fault characteristics may differ from those in traditional AC grid, which may lead to the failure of traditional pilot protections. And the DC system's control mode makes the inverter exhibit nonlinear characteristics in response to disturbances. The Tellegen's quasi-power theorem is derived based on Kirchhoff's Current Law (KCL) and Kirchhoff's Voltage Law (KVL), and is only related to circuit topology, independent of the branch content. It can be applied in lumped circuit, regardless of that the branch content is time-varying, time invariant, linear and nonlinear components. This paper applies the second theorem of Tellegen to the receiving AC system of LCC-HVDC. Based on the phasors of prefault and postfault voltage and current at both sides, this paper proposes a new pilot protection applying Tellegen theorem. It can accurately distinguish between internal and external faults and more applicable to receiving-end AC system of LCC-HVDC. The method's feasibility is verified by using PSCAD.