Effects of zero-sequence mutual inductance on zero-sequence pilot protection of parallel lines

Effects of mutual inductance on zero-sequence pilot protection of parallel lines are analyzed.Using a general model of mutual inductance lines and combining with the operating principle of the zero-sequence directional element,a detailed theoretical analysis is carried out on the actions of zero-sequence pilot protection under the conditions of inner fault and fault at the exit in the opposite direction.Studies show that in the case of internal fault or fault at the exit in the opposite direction,the zero-sequence directional protection of the fault line is immune to the impact of zero-sequence mutual inductance,and can operate correctly;the maloperation of the zero-sequence pilot protection of its parallel line depends on the tightness extent of electrical connection between the two mutual lines,the stronger the electrical connection is,the smaller the possibility of malfunction will be.At last,PSCAD simulation is carried out.