Inverse Time Overcurrent Protection - Toshiba GRL100-701B Instruction Manual

71
EF
EF_INST_TP
1634
+
[EFBTAL]
+
"O N"
EF_BLO CK
1591
72
EFI
[EFIBT]
+
"NO D", "F", "R"
EFI_BLO CK
1592
BUT_BLOCK
1550
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
• very inverse
• extremely inverse
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
OCI 0.5 - 25.0 A
( 0.10 - 5.00 A
TOCI 0.05 - 1.00
TOCIR 0.0 – 10.0 s
[MOCI] Long/Std/Very/Ext
[OCIBT] ON/OFF
TEF
t 0
≥
1
0.00 – 10.00s
&
[EFBT]
"O N" &
&
1
&
1
1
IEC 60255-3
IEC 60255-3
IEC 60255-3
Step
0.1 A
0.01 A
0.01
0.1 s
 84 
115 EF TRIP
&
EFBT (Alarm )
116
&
117 EFI TRIP
&
Default Remarks
10.0 A
2.00 A) (*)
0.50 OCI time setting
0.0 s OCI definite time reset delay
Std OCI inverse characteristic selection
ON OCI backup protection
6 F 2 S 0 8 5 0
118
BU-TRIP
1
≥