- 101 -
= lagging angle of I to Vp
θ = directional angle setting
Figure 2.10-9 Directional element
For the element for the fault in phase-bc, the polarizing voltage (Vp
bc
) is given using
Equation (2.10-29):
For the element for the fault in phase-a, the polarizing voltage (Vp
a
) is given using
Equation (2.10-30):
where,
V
0
= voltage in zero-sequence
Va = voltage in phase-A
Vbc = voltage in phase-bc
In Equation (2.10-29), the Vp
bc
voltage is subject to the memory action if the close-in
fault occurs in three-phases; that is, the values of the Va and Vbc voltages are set from the pre-
fault voltages. The memory is retained for two cycles after the fault occurs. Note that the
polarizing voltage (Vpa) in Equation (2.10-30) is not subject to the memory action.
If a close-in fault in three-phases occurs, the Quad element can be enhanced for an offset
Quad element, as shown in Figure 2.10-10. Similar to issuing the instantaneous trip signal for
the close-in three-phase fault, this enables the Quad element to issue a trip signal with a
delayed time together using the memory action.
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