-1 -0.5 0 0.5 1 1.5-1-0.8-0.6-0.4-0.200.20.40.60.81------------------------------------------------------------------------------------------------------------------------Real part (R) of Z in Ohms →Imaginary part (X) of Z in Ohms →^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^------------------------------- --------------- - ---------------GrelayrelayfaultREX [Ohm]SEX-line →limit ofreachzone 2zone 1Z(R,X) 20 msafter line outthis circle formsthe right-hand sideedge of the lens06pre-faultZ(R,X)512340 → pre-fault Z(R, X)3 → Z(R, X) under fault5 → Z 20 ms after line out6 → pow er line reclosedRSE RElens →110°Z-line→fault→IEC10000111-1-en.vsdIEC10000111 V1 ENFigure 78: A stable case where the disturbance does not make the generator to goout-of-stepIt shall be observed that for a stable case, as shown in Figure 78, where the disturbancedoes not cause the generator to lose step, the complex impedance Z(R, X) exits the lenscharacteristic on the same side (point 4) it entered it (point 2), and never re-enters the lens.In a stable case, where the protected generator remains in synchronism, the compleximpedance returns to quadrant 1, and, after the oscillations fade, it returns to the initialnormal load position (point 0), or near.7.4.7.1 Lens characteristicA precondition in order to be able to construct a suitable lens characteristic is that thepower system in which OOSPPAM (78) is installed, is modeled as a two-machineequivalent system, or as a single machine – infinite bus equivalent power system. Then theimpedances from the position of OOSPPAM (78) in the direction of the normal load flow(that is from the measurement point to the remote system) can be taken as forward. Thelens characteristic, as shown in Figure 76 and Figure 78, is obtained so that two equal insize but differently offset Mho characteristics are set to overlap. The resultant lenscharacteristic is the loci of complex impedance Z(R, X) for which the rotor (power) angleis constant, for example 110 degrees or 120 degrees; these are the angles where stabilityproblems are very likely. Figure 79 illustrates construction of the lens characteristic for apower system.Section 7 1MRK 502 048-UUS AImpedance protection180Technical manual
