9-6 D60 Line Distance Protection System GE Multilin9.1 DISTANCE ELEMENTS 9 THEORY OF OPERATION99.1.4 MEMORY POLARIZATIONAll distance functions use memory polarization. The positive-sequence voltage – either memorized or actual – is used as apolarizing signal. The memory is established when the positive-sequence voltage remains above 80% of its nominal valuefor five power system cycles. The memory voltage is a three-cycle old voltage.Once established, the memory is applied for the user-specified time interval. The memory timer is started when the voltagedrops below 80% of nominal or when the user-programmable condition is asserted to force memory polarization. After thememory expires, the relay checks the magnitude of the actual positive-sequence voltage. If it is higher than 10% of nomi-nal, the actual voltage is used; if lower, the memory voltage continues to be used.A provision is added to force self-polarization from any user-programmable condition.The memory-polarized mho has an extra directional integrity built-in as illustrated below. The self-polarized mho character-istic is shifted in the reverse direction for a forward fault by an amount proportional to the source impedance, and in the for-ward direction for a reverse fault.Table 9–4: DIRECTIONAL QUADRILATERAL GROUND DISTANCE FUNCTIONSCHARACTERISTIC COMPARATOR INPUTS LIMIT ANGLEReactance I Z – V j I_0 e j or j I_2 e j COMP LIMITDirectional I_0 Z D V_1M DIR COMP LIMITDirectional I_2 Z D V_1M DIR COMP LIMIT (removed when 3I_0 > OC SUPVand I_2 < CUTOFF)Right Blinder I Z R – V I Z R 90°Left Blinder I Z L – V I ZL 90°Fault-type I_0 I_2 50° (removed during open pole conditions or when3I_0 > OC SUPV and I_2 < CUTOFF)Zero-sequence I_0 Z D –V_0 90° (zones and higher only; removed for zones 2 andhigher during open pole conditions)Table 9–5: NON-DIRECTIONAL MHO PHASE DISTANCE FUNCTIONSCHARACTERISTIC COMPARATOR INPUTS LIMIT ANGLEOffset mho I Z – V I Z REV – V COMP LIMITTable 9–6: NON-DIRECTIONAL MHO GROUND DISTANCE FUNCTIONSCHARACTERISTIC COMPARATOR INPUTS LIMIT ANGLEOffset mho I Z – V I Z REV – V COMP LIMITFault-type I_0 I_2 50° (removed during open pole conditions or when 3I_0 > OCSUPV and I_2 < CUTOFF)Table 9–7: NON-DIRECTIONAL QUADRILATERAL PHASE DISTANCE FUNCTIONSCHARACTERISTIC COMPARATOR INPUTS LIMIT ANGLEForward Reactance I Z – V I Z COMP LIMITReverse Reactance I Z REV – V I ZREV COMP LIMITRight Blinder I Z R – V I Z R 90°Left Blinder I Z L – V I ZL 90°Table 9–8: NON-DIRECTIONAL QUADRILATERAL GROUND DISTANCE FUNCTIONSCHARACTERISTIC COMPARATOR INPUTS LIMIT ANGLEForward Reactance I Z – V j I_0 e j or j I_2 e j COMP LIMITReverse Reactance I Z REV – V –j I_0 e j or –j I_2 e j COMP LIMITRight Blinder I Z R – V I Z R 90°Left Blinder I Z L – V I ZL 90°Fault-type I_0 I_2 50° (removed during open pole conditions orwhen 3I_0 > OC SUPV and I_2 < CUTOFF)
