GE G30 Instruction Manual page 512

CONTROL ELEMENTS
5
5.8.12.4 VT fuse failure
SETTINGS  CONTROL ELEMENTS  MONITORING ELEMENTS  VT FUSE FAILURE 1(4)
 VT FUSE FAILURE 1

Every signal source includes a fuse failure scheme.
The VT fuse failure detector is used to raise an alarm and/or block elements that operate incorrectly for a full or partial loss
of AC potential caused by one or more blown fuses. Some elements that can be blocked (via the BLOCK input) are distance,
voltage restrained overcurrent, and directional current.
There are two classes of fuse failure that 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. Also, a rapid decrease in the phase voltages magnitude from a healthy
voltage level without disturbance in current can indicate VT fuse fail conditions. These noted indications of fuse failure can
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 provided.
Once the fuse failure condition is declared, it is sealed-in until the cause that generated it disappears.
5-298
Figure 5-166: CT failure detector logic
VT FUSE FAILURE 1

FUNCTION: Disabled
VT FUSE FAILURE 1

ALARM DELAY: 1.000 s
NEUTRAL WIRE OPEN 1

DETECTION: Disabled
NEUTRAL WIRE OPEN 1

3 HARM PKP: 0.100 pu
Range: Disabled, Enabled
Range: 0.000 to 65.535 s in steps of 0.001
Range: Disabled, Enabled
Range: 0.004 to 3.000 pu in steps of 0.001
G30 GENERATOR PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 5: SETTINGS