Schweitzer the engineering laboratory (SEL) microcomputer line protection has used the belt compensation negative sequence impedance directional element. In negative sequence impedance plane, when has the asymmetric failure, if actual surveys negative sequence impedance Z2=U2/I2 (in the formula U2, I2 respectively be inputs relay's breakdown voltage, electric current negative sequence component) the spot falls in z2=Z2Fb (in the formula z2 is survey negative sequence impedance in line negative sequence anti-angle direction projection, Z2Fb is forward movement threshold value which SEL relay basis different Z2 calculates) when the curve breast (z2≤Z2Fb) distinction for the direction breakdown, falls, in z2=Z2Rb (in the formula Z2Rb is backward action threshold value which SEL relay basis different Z2 calculates) when the curve upper side (z2≥Z2Rb) distinction for reversed direction breakdown. This kind of negative sequence directional element's installation value and movement characteristic and equipment movement actual system negative sequence impedance related, therefore when to uses this kind of negative sequence directional element's protection carries on the relay examination, the experiment, should pay attention to the testing method, if with the examination tradition relay's testing method, will possibly meet some questions.
