84
6
F
2
S
0
8
5
0
"ON"
[EFBT]
+
1
EF_BLOCK
1591
&
EFBT (Alarm )
116
"ON"
[EFBTAL]
+
&
&
EFI_BLOCK
1592
1
&
"NOD", "F", "R"
[EFIBT]
+
1
BUT_BLOCK
1550
&
EF TRIP
115
EFI
72
&
EFI TRIP
117
&
EF_INST_TP
1634
BU-TRIP
118
1
≥
EF
TEF
t
0
0.00 – 10.00s
71
1
≥
Figure 2.5.2 Overcurrent Backup Protection EF and EFI
2.5.1 Inverse Time Overcurrent Protection
In a system in which the fault current is mostly determined by the fault location, without being
greatly affected by changes in the power source impedance, it is advantageous to use the inverse
definite minimum time (IDMT) overcurrent protection. Reasonably fast tripping should be
obtained even at a terminal close to the power supply by using the inverse time characteristics. In
the IDMT overcurrent protection function, one of the following three IEC-standard-compliant
inverse time characteristics and one long time inverse characteristic is available.
•
standard inverse
IEC 60255-3
•
very inverse
IEC 60255-3
•
extremely inverse
IEC 60255-3
The IDMT element has a reset feature with definite time reset.
If the reset time is set to instantaneous, then no intentional delay is added. As soon as the
energising current falls below the reset threshold, the element returns to its reset condition.
If the reset time is set to some value in seconds, then an intentional delay is added to the reset
period. If the energising current exceeds the setting for a transient period without causing
tripping, then resetting is delayed for a user-definable period. When the energising current falls
below the reset threshold, the integral state (the point towards operation that it has travelled) of
the timing function (IDMT) is held for that period.
This does not apply following a trip operation, in which case resetting is always instantaneous.
Setting
The following table shows the setting elements necessary for the inverse time overcurrent
protection and their setting ranges.
Element Range
Step Default Remarks
OCI
0.5 - 25.0 A
0.1 A
10.0 A
( 0.10 - 5.00 A
0.01 A
2.00 A) (*)
TOCI
0.05 - 1.00
0.01
0.50
OCI time setting
TOCIR
0.0 – 10.0 s
0.1 s
0.0 s
OCI definite time reset delay
[MOCI]
Long/Std/Very/Ext
Std
OCI inverse characteristic selection
[OCIBT]
ON/OFF
ON
OCI backup protection
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