Toshiba GRL100-701B Instruction Manual page 86

EFI 0.5 - 5.0 A
( 0.10 - 1.00 A
TEFI 0.05 - 1.00
TEFIR 0.0 – 10.0 s
[MEFI] Long/Std/Very/Ext
[EFIBT] OFF/NOD/F/R
(*) Current values shown in the parentheses are in the case of 1 A rating. Other current values are in
the case of 5 A rating.
The scheme switches [MOCI] and [MEFI] are used to select one of the four inverse time
characteristics.
Current setting
In Figure 2.5.1.1, the current setting at terminal A is set lower than the minimum fault current in
the event of a fault at remote end F1. Furthermore, when considering also backup protection of a
fault within the adjacent lines, it is set lower than the minimum fault current in the event of a fault
at remote end F3. For grading of the current settings, the terminal furthest from the power source
is set to the lowest value and the terminals closer to the power source are set to a higher value.
The minimum setting is restricted so as not to operate on false zero-sequence currents caused by
an unbalance in the load current, errors in the current transformer circuits or zero-sequence
mutual coupling of parallel lines.
Figure 2.5.1.1 Current Settings in Radial System
Time setting
Time setting is performed to provide selectivity in relation with the relays on the adjacent lines.
Suppose a minimum source impedance when the current flowing in the relay becomes the
maximum. In Figure 2.5.1.1, in the event of a fault at near end F2 of the adjacent line, the
operating time is set so that terminal A may operate by time grading Tc behind terminal B. The
current flowing in the relays may sometimes be greater when the remote end of the adjacent line
is open. At this time, time coordination must also be kept.
The reason why the operating time is set when the fault current reaches the maximum is that if
time coordination is obtained for large fault current, then time coordination can also be obtained
for small fault current as long as relays with the same operating characteristic are used for each
terminal.
The grading margin Tc of terminal A and terminal B is given by the following expression for a
fault at point F2 in Figure 2.5.1.1.
Tc = T1 + T2 + M
where, T1: circuit breaker clearance time at B
T2: relay reset time at A
M:
When single-phase autoreclose is used, the minimum time of the earth fault overcurrent
protection must be set longer than the time from fault occurrence to reclosing of the circuit
breaker. This is to prevent three-phase final tripping from being executed by the overcurrent
protection during a single-phase autoreclose cycle.
0.1 A 5.0 A
0.01 A 1.00 A) (*)
0.01 0.50
0.1 s 0.0 s
Std
NOD
A
F1
margin
 85 
6 F 2 S 0 8 5 0
Earth fault EFI setting
EFI time setting
EFI definite time reset delay
EFI inverse characteristic selection
EFI backup protection
B
F2 F3
C