A novel method adapted to weak-infeed system for preventing mal-operation of the zero-sequence direction component

Mutual inductance between lines would cause mal-operation of the zero-sequence direction component. Differences of fault characteristics in three-phase current fault components between healthy lines and the fault line were analyzed and it was found out that three-phase current fault components of healthy lines are equal, while those of the fault line are quite different. In the weak-infeed operation mode, three-phase current fault components are approximately equal on the weak-infeed side of the fault line. Thus, the identification method using only current fault components is not applicative. To solve this problem, a comprehensive criterion consisting of both current and voltage error coefficients was constructed through analyzing differences of fault characteristics in three-phase current and voltage fault components between healthy lines and the fault line thoroughly under weak-infeed operation condition. PSCAD-based simulation results show that the comprehensive criterion is reliable in identifying healthy lines and the fault line in both weak-infeed and not weak-infeed operation modes. Consequently, zero-sequence direction components of healthy lines can be blocked while those of the fault line are not blocked. In the proposed method using both current and voltage error coefficients, only single-loop and single-ended electrical quantities are needed. In addition, the method is capable of automatically identifying electromagnetic situation of the lines. Thus, it is of practical value.