A novel method for preventing mal-operation of the zero-sequence directional component

Zero-sequence directional components of the healthy line would incorrectly discriminate the fault direction, causing mal-operation of the pilot zero-sequence directional protection, due to the influence of mutual inductance between lines under weak current and strong magnetic situations. In this paper, the correct working conditions of the zerosequence directional component are analysed and the difference in fault characteristics between the fault and healthy line is obtained by comparing the electrical quantities. The fault components of the three-phase currents are found the same in the healthy line, while they are quite different in the fault line. By identifying the status of lines with error coefficient formula, a novel blocking method is proposed to prevent mal-operation of the zero-sequence directional component. For the healthy line, zero-sequence directional components at both ends can be blocked, while they are not blocked in the fault line. The effectiveness of the proposed method is tested with a model of double-circuit transmission system on the same tower built on the PSCAD platform. Simulation results show that the method is reliable in identifying the status of the lines with high sensitivity. The proposed method is capable of identifying the mutual inductance between transmission lines under weak current and strong magnetic situations. Thus, it is practical in real transmission systems.