一 种 适 用 于 混 合 双 极 直 流 输 电 的 纵 联 方 向 保 护 方 法

DC transmission lines usually take large inductance and DC filters as the boundary. When a fault traveling wave undergoes refraction and reflection at the boundary，its traveling wave energy will also be absorbed due to the inductance and DC filters，resulting in the difference of high-frequency traveling wave energy within and outside the region. When the positive direction fault occurs，the energy of the high-frequency forward traveling wave is less than that of the high-frequency backward traveling wave. When the opposite direction fault occurs，the energy of the high-frequency forward traveling wave is greater than that of the high-frequency backward traveling wave. Based on this feature，a pilot directional protection based on the difference of high-frequency energy of forward and backward traveling waves is proposed that uses the wavelet packet transform algorithm to extract the high-frequency energy of the traveling wave，and uses the difference of the high-frequency energy of the forward and backward traveling waves to distinguish the faults inside and outside the area. The simulation results show that the protection can quickly and accurately identify faults，and is not affected by fault type，transition resistance，fault location distance，and noises. It has certain practicability.