Startco Engineering Ltd. Page 11
FPU-16 Feeder Protection Unit Rev. 1
Pub. FPU-16-M, November, 1997 Downloaded from the Internet, see Disclaimer.
Default Values:
Trip............................................. 25%
Alarm.......................................... 15%
3.6 MODE 4 — EARTH FAULT
This mode is used to enter earth-fault set points and to annunciate earth-fault
alarms and trips. Set points are expressed in percent of the earth-fault-CT-
primary rating entered in Mode 6.
Optional CT’s (EFCT-1 or EFCT-2) with 5-A-primary ratings are available for
sensitive earth-fault detection in applications where earth-fault current is less
than 100 A and surge current is less than 2.5 kA. If surge current is greater
than 1 kA but less than 2.5 kA, a flux conditioner should be used to prevent
nuisance tripping. If earth-fault current is greater than 100 A, surge current is
greater than 2.5 kA, or if a trip level greater than 5 A is required, use a 5-A- or
1-A-secondary earth-fault CT that will not saturate at the prospective currents.
Earth-fault current can be derived from the phase currents by using the ICT-2
residual connection. See Section 4.5.2. When this connection is used, the
primary rating of the earth-fault CT is the same as the phase CT's. Due to CT
errors, trip set points should be greater than 10% with the residual connection.
Earth-fault detection in a two-CT configuration requires an earth-fault CT. Do
not use a residual-type connection with two phase-CT's because an earth fault
in the derived phase will not be detected.
Four earth-fault-trip times are available. See Section 3.7.5 and Table 2.
Set-Point Range.................................... 1% to 100% of Earth-Fault-
CT-Primary Rating
Set-Point Step Size............................... 1%
Trip Time............................................... 3, 6, 12, or 24 cycles
Alarm Time............................................ 12 cycles
Trip-and-Alarm-Time Accuracy............... +3, -0 cycles
Display Codes:
Trip............................................. 4FFF
Alarm.......................................... 4AAA
Set Point Deleted........................ 4ddd
Default Values:
Trip Time .................................... 3 cycles
Trip Level.................................... 40%
Alarm Level................................. 20%
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