8-6 D30 Line Distance Relay GE Multilin8.1 DISTANCE ELEMENTS 8 THEORY OF OPERATION88.1.4 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.Figure 8–2: DYNAMIC SHIFT OF THE MHO CHARACTERISTICThe same desirable effect of memory polarization applies to the directional comparator of the quadrilateral characteristic.Table 8–6: 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°Table 8–7: 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 8–8: NON-DIRECTIONAL QUADRILATERAL GROUND DISTANCE FUNCTIONSCHARACTERISTIC COMPARATOR INPUTS LIMIT ANGLEForward Reactance I × Z – V j × I_0 × e jΘ or j × I_2 × e jΘ COMP LIMITReverse Reactance I × Z REV – V –j × I_0 × e jΘ or –j × I_2 × e jΘ 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°RMemory-polarized mho(Reverse fault)Memory-polarized mho(Forward fault)X837719A1.CDRSelf-polarized mho
