Based on the analysis of fault traveling wave characteristics at both ends of the line

a new algorithm of pilot protection based on the energy comparison of fault voltage direction traveling wave is proposed. The single frequency energy of voltage direction traveling wave is obtained based on S-transform within a period of time after the occurrence of the fault

the ratio of the voltage forward traveling wave energy on the side and the voltage backward traveling wave energy on the other side is used to construct the protection judgment. For the external fault

the smaller energy ratio is close to one

for the internal fault

the energy ratio is larger. Then the internal and external fault of transmission lines can be identified obviously. The simulation result shows that the internal and external fault can be distinguished accurately under the condition of smaller fault inception angle by the method presented in this paper

its performance is not affected by fault types

grounding resistance

fault location and bus configuration.