9-18 C70 Capacitor Bank Protection and Control System GE Multilin9.4 SETTING EXAMPLE 9 APPLICATION OF SETTINGS9Figure 9–13: VOLTAGE DIFFERENTIAL BLOCKING DURING VT FUSE FAILUREThe 87V-2 and 87V-3 differential elements for the strings against tap voltage are created in a similar manner. In thesecases, the K factor will be different, reflecting the voltage division of K = 463.8194 between the string and tap capacitor volt-ages.9.4.6 BANK PHASE CURRENT UNBALANCE SETTINGSTwo phase current unbalance (ANSI 60P) stages are used to provide trip and alarm levels during capacitor unit failures ineach differential element.The pickup setting for the stage 1 phase current unbalance alarm element is programmed for one element failure.(EQ 9.25)SRC2 VT FUSE FAIL OPSRC3 VT FUSE FAIL OPOR(2)= VTFF 87V-1 (VO1)SRC1 VT FUSE FAIL OPSRC2 VT FUSE FAIL OPOR(2)= VTFF 87V-2 (VO2)SRC1 VT FUSE FAIL OPSRC3 VT FUSE FAIL OPOR(2)= VTFF 87-3 (VO3)OR(2)OR(2)OR(2)= VTFF 87V-1 (VO1)= VTFF 87V-2 (VO2)= VTFF 87V-3 (VO3)843765A1.CDR60P alarm 0.9I unbal f1_max( ) 0.9 0.0209 pu× 0.019 pu= = =
