GE Power ManagementL90 Line Differential Relay5-1475 SETTINGS 5.6 CONTROL ELEMENTS55.6.11 VT FUSE FAILUREPATH: SETTINGS ÖØ CONTROL ELEMENTS ÖØ MONITORING ELEMENTS ÖØ VT FUSE FAILUREEvery signal source includes a fuse failure scheme.The VT fuse failure detector can be used to raise an alarm and/or block elements that may operate incorrectly for a full orpartial loss of AC potential caused by one or more blown fuses. Some elements that might be blocked (via the BLOCKinput) are distance, voltage restrained overcurrent, and directional current.There are two classes of fuse failure that may occur: (A) loss of one or two phases, and (B) loss of all three phases. A dif-ferent means of detection is required for each class. An indication of class A failures is a significant level of negativesequence voltage, whereas an indication of class B failures is when positive sequence current is present and there is aninsignificant amount of positive sequence voltage. These noted indications of fuse failure could also be present when faultsare present on the system, so a means of detecting faults and inhibiting fuse failure declarations during these events is pro-vided. Once the fuse failure condition is declared, it will be sealed-in until the cause that generated it disappears.An additional condition is introduced to inhibit a fuse failure declaration when the monitored circuit is de-energized; positivesequence voltage and current are both below threshold levels.The common FUNCTION setting will Enable/Disable the fuse failure feature for all 6 sources.Figure 5–77: VT FUSE FAIL SCHEME LOGIC VT FUSE FAILUREVT FUSE FAILUREFUNCTION: DisabledRange: Disabled, Enabled827093A5.CDRVT FUSE FAILUREFUNCTION:V_2 > 0.25 p.u.V_1 < 0.05 p.u.V_1 < 0.7 p.u.I_1 > 0.075 p.u.I_1 < 0.05 p.u.RUNRUNRUNRUNRUNSETTINGCOMPARATORSSOURCE 1FLEXLOGIC OPERANDFLEXLOGIC OPERANDDisabled=0Enabled=1SRC1 VT FUSE F OPSRC1 VT FUSE F DPOFUSE FAILFAULTSRC1 50DD OPANDANDANDANDANDANDORORORV_1I_1V_220 CYCLES0
