Toshiba GRZ100-211B, Instruction Manual

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6 F 2 S 0 8 3 4
To maintain stable operation for close-up three-phase faults which cause the voltages of all phases
to drop to 0 or close to 0, zone 1 for phase faults, once operated, changes its element to a reverse
offset element. This continues until the fault is cleared, and thus it is effective for time delayed
protection.
The reactance element characteristics of zone 1, zone 1 extension, zone 2, zone F and zone R1 are
parallel lines to the R axis and provide sufficient coverage for high-resistance faults. The reactance
element characteristics of zone 1 and zone 1 extension can be transformed to a broken line
depending on the load flow direction in order to avoid overreaching by the influence of load
current. The characteristic in the resistive direction is limited by the mho characteristic of zone 3.
The reactive reach setting is independent for each zone. It is also possible to have independent
settings for each individual phase fault and earth fault elements.
With a long-distance line or heavily loaded line, it is possible for the load impedance to encroach
on the operation zone of the mho element. Blinders are provided to limit the operation of the mho
element in the load impedance area.
Zero-sequence current compensation is applied to zone 1, zone 2 and reverse zone R1 for earth
fault protection. This compensates measuring errors caused by the earth return of zero-sequence
current. This allows the faulted phase reactance element to precisely measure the
positive-sequence impedance up to the fault point. Furthermore, in the case of double-circuit lines,
zero-sequence current from the parallel line is introduced to compensate for influences from
zero-sequence mutual coupling. (R1 is not provided with zero sequence mutual coupling
compensation for the parallel line.) Considering the case where the impedance angle of
positive-sequence impedance and zero-sequence impedance differ which is the most common in
cable circuits, GRZ100 carries out vectorial zero-sequence current compensation.
The autoreclose schemes are utilised with instantaneous zone 1 tripping. When single-phase
autoreclose or single- and three-phase autoreclose are selected, zone 1 executes single-phase
tripping for a single-phase earth fault. In order to achieve reliable fault phase selection even for
faults on heavily loaded long-distance lines or irrespective of variations in power source
conditions behind the relaying point, an undervoltage element with current compensation is used
as a phase selector. Other zones only execute three-phase tripping, and do not initiate autoreclose.
2.4.1.2 Scheme Logic
Figure 2.4.1.5 shows the scheme logic for the time-stepped distance protection. For zone 1
tripping, as described later, it is possible to select instantaneous tripping or time delayed tripping
using the scheme switch [Z1CNT] in the trip mode control logic. (Detail of the [Z1CNT] is
described after.) Zone 2, zone 3, zone F, zone R1, zone R2 and zone ND give time delayed
tripping. However, these zones can trip instantaneously by PLC signals Z
∗
_INST_TP. Timers
TZ2, TZ3, TZF, TZR1, TZR2 and TZND with time delayed tripping can be set for earth faults and
phase faults separately. Zone F, zone R1, zone R2 and zone ND backup tripping can be disabled
by the scheme switch [Z
∗
BT].
Note: For the symbols used in the scheme logic, see Appendix L.
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