GE L90 Instruction Manual page 377

5 SETTINGS
f) VT FUSE FAILURE
PATH: SETTINGS CONTROL ELEMENTS
VT FUSE FAILURE 1
Every 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 or
partial loss of AC potential caused by one or more blown fuses. Some elements that might be blocked (via the
are distance, voltage restrained overcurrent, and directional current.
There are two classes of fuse failure that may occur:
• Class A: loss of one or two phases.
• Class B: loss of all three phases.
Different means of detection are required for each class. An indication of Class A failures is a significant level of negative
sequence voltage, whereas an indication of class B failures is when positive sequence current is present and there is an
insignificant amount of positive sequence voltage. These noted indications of fuse failure could also be present when faults
are 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; positive
sequence voltage and current are both below threshold levels.
The function setting enables and disables the fuse failure feature for each source.
SETTING
Function
Disabled = 0
Enabled = 1
COMPARATORS
SOURCE 1 Run
V_2
V_1 Run
I_1
Run
Run
Run
FLEXLOGIC OPERANDS
SRC1 50DD OP
OPEN POLE OP
The OPEN POLE OP operand is applicable
to the D60, L60, and L90 only.
GE Multilin
MONITORING ELEMENTS
VT FUSE FAILURE 1
FUNCTION: Disabled
V_2 > 0.1 pu
OR
V_1 > 0.05 pu
AND
I_1 > 0.075 pu
TIMER
V_1 < 0.80 pu
2 cycles
AND
I_1 < 0.05 pu
20 cycles
AND
OR
AND
AND
Figure 5–134: VT FUSE FAIL SCHEME LOGIC
L90 Line Current Differential System
5.7 CONTROL ELEMENTS
VT FUSE FAILURE 1(4)
Range: Disabled, Enabled
AND
Reset-dominant
SET
OR
FAULT
Latch
AND
RESET
AND
OR SET
FUSE
FAIL
AND
Latch
RESET
Reset-dominant
input)
BLOCK
5
FLEXLOGIC OPERANDS
SRC1 VT FUSE FAIL OP
SRC1 VT FUSE FAIL DPO
FLEXLOGIC OPERAND
SRC1 VT FUSE FAIL VOL LOSS
827093AL.CDR
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