Toshiba GRZ100 B Series, Instruction Manual

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6 F 2 S 0 8 4 6
Directional element
The directional element is used for the quadrilateral four zone characteristics.
Vp
θ
I
lag
Figure 2.5.1.10 Directional Element
The characteristic of the directional element is obtained by the following equation.
I
･
Vp cos (
θ − φ
)
≥
0
where,
I = fault current
Vp = polarizing voltage
φ
= lagging angle of I to Vp
θ
= directional angle setting
The polarizing voltage Vp is the same one as employed in the mho element.
For B-to-C-phase phase fault element
Vpbc = 3 (Va
−
V0)
∠ −
90
°
+ Vbc
For an A-phase earth fault element
Vpa = 3 (Va
−
V0) + Vbc
∠
90
°
where,
Va = A-phase voltage
V0 = zero-sequence voltage
Vbc = B-to-C-phase voltage
The polarizing voltage for the phase fault element has a memory action for the close-up
three-phase fault. Va and Vbc mentioned above are the memorized pre-fault voltages. This
memory is retained for two cycles after a fault occurs. The polarizing voltage for the earth fault
element has no memory action.
When a three-phase fault occurs within zone 1, the phase fault element for zone 1 is modified to an
offset characteristic as shown in Figure 2.5.1.11. This, together with voltage memory action,
enables zone 1 to perform tripping with a time delay as well as instantaneous tripping for the
close-up three-phase fault.
The Z1X, Z2, ZF and Z3 do not have the modifying function mentioned above.