GE L90 Instruction Manual page 404

5.7 CONTROL ELEMENTS
g) 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.
5
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.
5-258
MONITORING ELEMENTS
VT FUSE FAILURE 1
FUNCTION: Disabled
NEUTRAL WIRE OPEN 1
MESSAGE
DETECTION: Disabled
NEUTRAL WIRE OPEN 1
MESSAGE
3 HARM PKP: 0.100
L90 Line Current Differential System
VT FUSE FAILURE 1(4)
Range: Disabled, Enabled
Range: Disabled, Enabled
0.000 to 3.000 pu in steps of 0.001
5 SETTINGS
input)
BLOCK
GE Multilin