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S4 CONTROLS
VT fuse fail (VTFF or 60VTS)
VOLTAGE INPUTS
V
(
V
)
a
ab
V
(
V
)
b
bc
V
V
(
)
c
ca
VOLTAGE INPUTS
V
V
(
)
a
ab
V
(
V
)
b
bc
V
V
(
)
c
ca
SETTING
Fuse Fail Function
= Disabled
NOTE: The VTFF uses phase to neutral voltages
phase-phase voltages
6–154
The 350 relay includes one VT Fuse Failure element. The measured voltages from the
installed phase VTs are monitored and compared against user programmable levels. If one
or two of the three voltages drops to less than 70% of nominal, and at the same time any
of the three voltages is greater than 85%, either an Alarm or a Trip will occur after a
1 second delay. The 70% threshold allows for the possibility that the downstream voltage
from a blown fuse is pulled up above zero by devices connected between the open fuse
and another phase. The VT reference for the VTFF element is the phase to neutral voltage
for Wye-connected VTs, and the phase-phase voltage for a Delta-connected VT. The VT
Connection, VT Ratio and VT Secondary voltage are user programmable values under
SETPOINTS > S2 SYSTEM SETUP > VOLTAGE SENSING
PATH:
SETPOINTS > S4 CONTROL > VT FUSE FAILURE
FUSE FAIL FUNCTION
Range: Disabled, Alarm, Trip
Default: Trip
For details see
Common
Figure 6-65: Fuse Fail Protection Logic Diagram
< 70%
< 70%
OR
< 70%
AND
> 85%
> 85%
OR
> 85%
= Alarm
= Trip
,
and
V
V
a
b
,
and
when "Delta" type is selected comparators.
V
V
V
ca
ab
bc
setpoints.
1 s
0
Command
RESET
when "Wye" VT type is selected under Voltage Sensing/VT connections setpoint, and uses
V
c
350 FEEDER PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 6: SETPOINTS
.
LOGIC OPERAND
Fuse Fail
LOGIC OPERAND
AND
Fuse Fail Alarm OP
Any Alarm OP
TARGET MESSAGE
Fuse Fail Alarm
State: Operate
Fuse Fail Trip
State: Operate
AND
S
LOGIC OPERAND
LATCH
Fuse Fail Trip OP
Any Trip OP
R
Set Dominant
898802A1.cdr
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