Study on A New Earth-fault Distance Protection for Four-circuit Transmission Lines on The Same Tower

Since the transmission corridors are becoming more and more valuable and the demand for transmission capacity is continually increasing, the four-circuit transmission lines on the same tower have been used more and more in the, high-voltage system. For this complex transmission system, there is an unpredictable mutual inductance error when measures the impedance, which will potentially cause the mal-operation of relay. Therefore, it is not feasible to use the traditional earth-fault distance protection in case of the single phase to earth fault. In this paper, twelve-sequence components method is introduced to decouple mutual electromagnetic effect between four-parallel transmission lines. Based on the analysis of the features of each component, the relationship between fault voltage and the current is presented. Furthermore, a new protection criterion for earth-fault distance protection is proposed. The new method has high sensitivity and reliability under different scenarios.