Toshiba GRL100-701B Instruction Manual page 54

6 F 2 S 0 8 5 0
• Line protection of adjacent lines
• Remote end breaker failure protection
Zone 3 setting
Zone 3, in cooperation with zone 2, affords backup protection for faults that have occurred on
adjacent lines. The reach should be set to exceed the remote end of the longest adjacent line
whenever possible. It is also necessary to take into account the effect of fault infeed at the remote
busbars. If an ideal reach setting as shown in Figure 2.3.1.8 is possible, the timer setting for zone 3
needs only to consider the coordination with the timer setting in zone 2 of the protected lines and
adjacent lines.
However, as shown in Figure 2.3.1.10, if there are short-distance adjacent lines and it is
impossible to establish coordination only by the reach setting, there may also be a case where the
time delay for zone 3 will need to be set greater than that of the adjacent lines.
The zone 3 reach is set on the characteristic angle when the mho characteristic is selected or set on
the X axis when the quadrilateral characteristic is selected.
Zone 3
T3'
Zone 3
T3
Zone 2
Zone 2
Zone 1
Zone 1
A B C
D
Figure 2.3.1.10 Zone 3 Setting (When one of the adjacent lines is very short)
Zone R setting
Zone R is used to provide local backup protection equivalent to that of zone 3 of the remote
terminal. In such a case, the reach is set so as to exceed the remote end of the longest adjacent line
behind the relaying point. The time delay is also set to be equivalent to that of the remote terminal.
the X axis when the quadrilateral characteristic is selected.
Z4 setting
Zone 4 is the reverse fault detection for the command protection. The reach setting of zone 4
should be greater than that of zone 2 or zone 3 whichever is used as a forward overreaching
element at the remote terminal.
The zone 4 reach is set on the characteristic angle when the mho characteristic is selected or set on
the X axis when the quadrilateral characteristic is selected.
Blinder setting
BFR and BRR reaches are set to the minimum load impedance with a margin. The minimum load
impedance is calculated using the minimum operating voltage and the maximum load current.
The blinder element (BFR) can be provided for each forward zone. The setting of blinder element
can be set independently or set common to forward zones by [BLZONE]=IND or
[BLZONE]=COM setting. In the [BLZONE]=IND setting, the forward zone blinder setting
should be set BFR1∗≤BFR2∗≤BFR∗. If BFR∗≤BFR1∗, for example, the reach of BFR1∗ is
 53 