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DIAC / DIFC / DSFC Digital Overcurrent Protection
PRODUCT DESCRIPTION
General
The DIAC, DIFC and DSFC are a family of self-
powered, single-phase, digital overcurrent relays.
The DIAC is packaged in a GE S1 style case, the
DIFC is packaged in a GE C1 style case and the
DSFC is packaged in a GE V1 style case. See the
HARDWARE DESCRIPTION section for mounting
dimensions.
The table below gives the model number break-
down.
D_ _CA _ _
B
Revision
1
1 Amp Nominal Current
5
5 Amp Nominal Current
IF
C1 case
IA
S1 case
SF
V1 case
These relays use waveform sampling of the current
input together with appropriate algorithms to pro-
vide a time overcurrent (TOC) and an instantane-
ous overcurrent (IOC) function.
Application
Time and instantaneous overcurrent functions are
widely used in many applications throughout the
power system. Typical examples are protection of
utility and industrial feeders and short circuit and
overload protection for transformers, and motors.
For feeder protection, the usual application re-
quires one relay per phase and a fourth relay con-
nected in the residual circuit of three ‘wye’ con-
nected current transformers (CTs). A typical exter-
nal connection diagram for this application is
shown in Figure 18 OR 19. Use of a separate
ground relay provides more sensitive protection for
ground faults.
The TOC reset characteristics can be set to emu-
late those of an induction disk or set for fast reset
with no intentional delay.
Functions
The TOC function operates on an ‘RMS’ current
calculated from the sampled values. The IOC func-
tion operates on the sampled values, and the algo-
rithm virtually eliminates the decaying DC offset
component to achieve low transient overreach of
less than 7%.
The relays contain two independent settings, one
for TOC and one for IOC.
TOC
The TOC function provides 16 selectable time cur-
rent curves.
•
IAC51
•
IAC53
•
55-SHORT TIME
•
57-MEDIUM TIME
•
66-LONG TIME
•
75-SHORT TIME
•
IAC77
•
95-SHORT TIME
•
IEC Inverse
•
IEC Very Inverse
•
IEC Extremely Inverse
•
IEEE Inverse
•
IEEE Very Inverse
•
IEEE Extremely Inverse
•
Definite Time
•
I
2
T
The IAC51, IAC53 and IAC77 curves match the
time current curve of the respective IAC model.
This includes the 0.5 through 9.9 time dial setting
and for both the 1 and 5 amp units. Numbered
curves 55, 57, 66, 75, and 95 match the shape of
the respective IAC model however the time dial
positions are not one to one equivalents. The IEC,
IEEE and I
2
t curves are based on the following
equations:
NOTE:
••••••••••••••••••••••••••••••••••
IEC equations are defined by IEC 255-4 and IEEE
equations are defined by IEEE PC37.112
••••••••••••••••••••••••••••••••••
In the following equations,
M = multiple of pickup
TD = time dial (0.5, 1, …, 9.9)
t = time (seconds)
Summary of Contents for DIAC
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