Paper Title
Reactive Energy Based HVDC Transmission Lines Protection

Due to the enhancement in power electronics application to power systems, high-voltage direct current (HVDC) transmission technology becomes a major contributor to power transmission.This protection scheme proposes a HVDC transmission line backup protection based on the reactive energy measurement in HVDC system. HVDC transmission systems mostly transmit active power under normal operating condition, whereas the reactive power flow on the DC transmission line is zeroneglecting some small harmonic components. The quantity of the harmonic reactive power on the DC line depends on the smoothing reactors and filtering effect of dc filters. The directional characteristics of reactive power flow is theoretically analyzed for internal and external faults and these characteristics will be used to construct a directional protection scheme. Hilbert transform is used for calculation of the reactive power. A bipolar 12-pulse HVDC system which based on the CIGRE benchmark is design using MATLAB/SIMULINK and extensive simulations of various faults situations are verified to test the effectiveness of the proposed scheme. Keywords— HVDC system, Hilbert Transform, Directional protection.