8-6 D60 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 ñ either memorized or actual ñ 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. After the memory expires, the relay checks the magnitude of the actual positive-sequencevoltage. If it is higher than 10% of nominal, the actual voltage is used; if lower, the memory voltage continues to be used.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 8ñ2: DYNAMIC SHIFT OF THE MHO CHARACTERISTICThe same desirable effect of memory polarization applies to the directional comparator of the quadrilateral characteristic.Table 8ñ6: NON-DIRECTIONAL MHO GROUND DISTANCE FUNCTIONSCHARACTERISTIC COMPARATOR INPUTS LIMIT ANGLEOffset mho I × Z ñ V I × Z REV ñ V COMP LIMITFault-type I_0 I_2 50∞ (removed during open pole conditions)Table 8ñ7: NON-DIRECTIONAL QUADRILATERAL PHASE DISTANCE FUNCTIONSCHARACTERISTIC COMPARATOR INPUTS LIMIT ANGLEForward Reactance I × Z ñ V I × Z COMP LIMITReverse Reactance I × Z REV ñ V I × ZREV COMP LIMITRight Blinder I × Z R ñ V I × Z R 90∞Left Blinder I × Z L ñ V I × ZL 90∞Table 8ñ8: NON-DIRECTIONAL QUADRILATERAL GROUND DISTANCE FUNCTIONSCHARACTERISTIC COMPARATOR INPUTS LIMIT ANGLEForward Reactance I × Z ñ V j × I_0 × e jΘ or j × I_2 × e jΘ COMP LIMITReverse Reactance I × Z REV ñ V ñj × I_0 × e jΘ or ñj × I_2 × e jΘ COMP LIMITRight Blinder I × Z R ñ V I × Z R 90∞Left Blinder I × Z L ñ V I × ZL 90∞Fault-type I_0 I_2 50∞ (removed during open pole conditions)RMemory-polarized mho(Reverse fault)Memory-polarized mho(Forward fault)X837719A1.CDRSelf-polarized mho
