Toshiba GR200 Series Instruction Manual

Also see for GR 200 Series: Instruction manual Instruction manual Instruction manual Instruction manual Instruction manual

6F2S1914 (0.49)GRL200 (Soft 033 & 037)- 117 -2.10.4 Common application for ZS and ZGApplications in ZS and ZG are divided into common features and special features. Each featuresecures this distance protection function.(i) Power swing blockOperation of power swing block (PSB)Power swings occur when the output voltages of generators located at different points in thepower system slip relative to one another because of system instabilities. This may be causedby sudden changes in load magnitude or direction, or by power system faults and theirsubsequent clearance. During the course of such a power swing, the impedance locus seen bythe distance protection relay may move (relatively slowly) from the load area into the operatingregion of the distance protection. Actually, the relay may see this phenomenon as a three-phasefault condition and may issue a trip signal if no countermeasure is applied. The majority ofpower swings are transient and the power system recovers after a short period. Since a tripsignal from the relay is undesirable in such cases, the function of power swing blocking (PSB)is provided enabling the operation of the distance protection to be blocked during the powerswing. Figure 2.10-24 illustrates a typical impedance locus as seen by the relay during thetransient power swing.Figure 2.10-24 Impedance locus during transient power swingAs shown in Figure 2.10-25 (a), for ZS, power swing blocking elements (PSBSOUT andPSBSIN) are formed as shown in the shaded area. As shown in Figure 2.10-25 (b), for ZG, thePSBGOUT and PSBGIN elements are provided with the similar characteristic and feature.Both PSB (PSBS and PSBG) functions do not operate when an earth fault overcurrent (EFL)element or a negative-sequence phase overcurrent (OCN-PS) element is operating. Note thatthe EFL and OCN-PS thresholds are defined with VCT rated value multiplied by 0.2 (i.e.,secondary rated 1A×0.2 or 5A×0.2).XRLoad AreaDistance protection zone (Mho char.)Impedance locusduring transientpower swing