Toshiba GRZ100 B Series, Instruction Manual, Page: 27 / 447

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6 F 2 S 0 8 4 6
Zone 1 is set to cover about 80% of the protected line. When GRZ100 is used as the main
protection, zone 1 generally provides instantaneous tripping but if used as a backup protection,
time delayed tripping can be provided. With the GRZ100, 5 types of zone 1 tripping modes can be
set using the trip mode setting switch.
Zone 2 is set to cover about 120% or more of the protected line, providing protection for the rest of
the protected line not covered by zone 1 and backup protection of the remote end busbar. In order
to coordinate the fault clearance time by the main protection, with the zone 1 protection of the
adjacent lines or by the remote end busbar protection, zone 2 carries out time delayed tripping.
Time
TR1
T3
T2
T1
C B A
Reverse Zone R1
Zone 2
Zone 1
Zone 3
∼
∼
Reverse Zone R2 TR2
TND
Zone ND Zone ND
(TF)
(Z3 or ZF)
Figure 2.4.1.3 Time/Distance Characteristics of Time-Stepped Distance Protection
Zone 3 is mainly provided for remote backup protection of adjacent lines. Its reach is set to at least
1.2 times the sum of the impedance of the protected line and the longest adjacent line. The zone 3
time delay is set so that it coordinates with the fault clearance time provided by zone 2 of adjacent
lines. (Z3 is applied to Zone 3. Z3 is also used for detection of forward faults in command
protection. If Z3 is dedicated to command protection, ZF can be used for Zone 3 instead of the Z3.)
The reverse looking zone R1 and R2 elements are used for time delayed local backup protection
for busbar faults and transformer faults. Furthermore, when applied to multi-terminal lines, it is
effective as the backup protection for adjacent lines behind the relaying point instead of the zone 3
protection at the remote terminal. This is because it is difficult for zone 3 at terminals A and C to
provide remote backup protection for the fault shown in Figure 2.4.1.4 due to fault infeed from the
other terminal, whereas reverse looking zone of terminal B is not affected by this.
Z4 element is used for reverse fault detection in command protection, but not for backup
protection.
The non-directional zone ND is used for time delayed backup protection including overall zones.
Zone 3
Zone R1
A
C
B
Figure 2.4.1.4 Reverse Zone Protection