P.3.142
SEL-411L Relay Protection Manual Date Code 20151029
Protection Functions
Ground Directional Element
Ground Directional Element
The relay offers a choice of three independent directional elements to
supervise the ground-distance elements and directional residual ground
overcurrent elements (67Gn, where n equals 1–4) during ground faults. You
can also use the ground directional element for torque control. Internal logic
selects the best choice automatically. Table 3.73 lists the directional elements
the relay uses to provide ground directional decisions.
The negative-sequence voltage polarized directional element 32QG listed in
Table 3.73 supervises the ground-distance elements and residual ground
directional overcurrent elements. The negative-sequence voltage polarized
directional element 32Q illustrated in Figure 3.92 only supervises the phase
distance elements.
The relay internal logic selects the best choice for directional supervision
according to prevailing power system conditions during the ground fault. The
logic determines the best choice for the ground directional element (32G)
from among the negative-sequence voltage-polarized directional element
(32QG), zero-sequence voltage-polarized directional element (32V), or the
zero-sequence current-polarized directional element (32I). The ground
directional element also supervises the quadrilateral ground-distance
elements.
During the single-pole open condition (SPO is a logical 1), the relay
supervises the ground directional element with an open pole directional
element. The purpose of this directional element is to ensure secure operation
of the distance elements during the single-pole open condition. The operation
of the single-pole open directional element is indicated by the 32SPOF and the
32SPOR Relay Word bits.
Because the single-pole open directional element may operate as a result of
unbalance currents generated during the single-pole open condition, it is
recommended that ground and negative-sequence overcurrent elements that
are used for single-pole tripping be supervised by the single-pole open
condition. To supervise overcurrent elements during the single-pole open
condition, set the element torque control equation (67GnTC or 67QnTC,
where n equals 1–4) equal to NOT SPO.
Settings
Table 3.74 lists the relay settings corresponding to the ground directional
element.
Table 3.73 Directional Elements Supervising Ground Elements
Directional
Elements
Description
Forward
Output
Reverse
Output
32QG Negative-sequence voltage polarized for
ground faults
F32QG R32QG
32V Zero-sequence voltage polarized F32V R32V
32I Zero-sequence current polarized F32I R32I
Table 3.74 Ground Directional Element Settings (Sheet 1 of 2)
Setting Description Range
Default
(5 A)
E32 Directional control Y, AUTO AUTO
ORDER Ground directional element priority combine Q, V, I QV
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