1. School of Electrical and Electronic Engineering, North China Electric Power University, Baoding 071003, China; 2. Maintaining Branch of State Grid Jibei Electric Power Company, Beijing 102488, China

The traditional method for fault location of T-type lines is not able to identify the fault section correctly when the fault occurs near the T-type node, thus failing to locate the fault. To solve this problem, a novel branch identification criterion algorithm is proposed based on the principle of equal positive sequence voltage detected at both ends. It is concluded that the fault location function is monotonical and at the head and end the two values differ by approximately 180° at the fault branch, but the fault location function is also monotonical and at the head and end the two values are approximately equal at the healthy branch. With the phase difference in magnitude between the fault location function at the head and that at the end as the criterion for fault branch, the fault distance is solved using the analytical expression for fault distance. This branch identification criterion algorithm has remedied the drawback of traditional fault location methods. Despite the dead zone of fault location, no type identification is required, while the fault distance is obtained simply by calculating a few points with the corresponding formula. With its simple procedure and fast implementation, the proposed algorithm accuracy is in theory independent of fault type, fault resistance at fault point and operation mode, etc. The EMTP simulation results verify the validity and high precision of the algorithm.