GE DIAC, Instruction Manual, Page: 38 / 46

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36 DIAC / DIFC / DSFC Digital Overcurrent Protection
INSTANTANEOUS UNIT
The Instantaneous unit is designed similarly to a
hinged armature instantaneous unit.
The
instantaneous unit will react differently
depending on how the signal is applied. If the
signal is applied suddenly with no prefault
current, the operating time will be longer. If a
prefault current is applied prior to the fault the
operating time will be shorter. The following test
determines that the instantaneous unit is working
correctly and confirms the operating time for
faults applied with no prefault current.
Connect the relay as shown in Figure 26 or 27,
Set the instantaneous unit pickup to 2 amps (5
amp rated relay) or 0.4 amps (1 amp rated relay)
with a zero IOC delay setting. Apply 6 amps (5
amp rated relay) or 1.2 amps (1 amp rated relay)
and measure the operating time. The operating
time should be between 32 ms and 46 ms. This
time is subject to dependent on the multiple of
pickup current and the fault incidence angle. A
graph of how the instantaneous unit varies as a
function of input current is provided in this book
for reference, Figure 17.
Target and
Seal-in
AUX TOC
contact
T11
T12
T2
T1
I
in
T5
T6
Single Phase
Current Source
Start
Stop
TIMER
– Negative
36/300VDC
Power Supply
Current Limited to
200 mA
+ Positive
Figure 24: DIFC Test Setup for Pickup and Operating Time Verification