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DIAC / DIFC / DSFC Digital Overcurrent Protection
23
CALCULATION OF SETTINGS
When replacing IAC, IFC or SFC relays, review
the time current curves of the digital relays to
verify that they conform to the relays being re-
placed. In some cases it may be necessary to
redo the coordination study to assure coordina-
tion with other devices.
The base time of the Definite Time Curve is 1
second. The base time is multiplied by the time
dial to provide the actual operating time. The
default or lowest time dial setting for the Definite
Time Curve is 0.1.
The I
2
T curve has a K value of 250 @ time dial
of 1. The range is from 25 to 2475 in steps of 25
set by the time dial. The default or lowest time
dial setting for the I
2
T curve is 0.1.
TOC pickup is settable from 0.5 to 15.9 amps in
0.1 amp increments for the 5 amp model, and
0.1 to 3.18 amps in 0.02 amp increments for the
1 amp model, a setting of 0 disables the TOC
element. The time dial can be set from 0.5 to 9.9
in 0.1 increments on both the 5 amp model and
the 1 amp model. The only exception is for the
Definite Time and I2T curves where 0.1 is the
minimum value.
The IOC function is settable from 1 to 159 amps
in 1 amp increments for the 5 amp model, and
0.2 to 31.8 amps in increments of 0.2 amps for
the 1 amp model. Setting the pickup to 0 dis-
ables the IOC element. Both models have an
IOC delay adjustment from 50 to 400 millisec-
onds in 25 millisecond steps.
The formula: IOC delay in milliseconds = DS x
25 + 25, where DS is setting on IOC delay dial.
The TOC reset characteristic can be controlled
from the front panel. The TOC reset can be set
to “timed reset” which emulates the characteris-
tic of an induction disk relay, or “instantaneous
reset” where the reset is fixed at 40 to 50 milli-
seconds.
The system frequency can be set for 50 or 60 Hz
controlled from the front panel.
Summary of Contents for DIAC
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