4.40
SEL-351A Relay Instruction Manual Date Code 20080213
Loss-of-Potential, Load Encroachment, and Directional Element Logic
Directional Control Settings (Not in SEL-351A-1)
In most communications-assisted trip schemes, the levels are set as follows:
➤ Level 1 overcurrent elements set direction forward (DIR1 = F)
➤ Level 2 overcurrent elements set direction forward (DIR2 = F)
➤ Level 3 overcurrent elements set direction reverse (DIR3 = R)
In some applications, level direction settings DIR1–DIR4 are not flexible
enough in assigning the desired direction for certain overcurrent elements.
Directional Control Provided by Torque Control Settings (Not in SEL-351A-1)
on page 4.57 describes how to avoid this limitation for special cases.
ORDER—Ground Directional Element Priority Setting
Setting ORDER can be set with the elements listed and defined in Table 4.1,
subject to the setting combination constraints in Table 4.2 and Tab le 4.3 . Note
that Table 4.1 and Table 4 .2 also list directional element availability per model
(according to the neutral channel [IN] rating). Table 4.3 lists the ground
directional element availability as a result of the voltage connection settings.
The order in which the directional elements are listed in setting ORDER
determines the priority in which these elements operate to provide Best
Choice Ground Directional Element logic control.
For example, if setting:
ORDER = QVS
then the first listed directional element (Q = negative-sequence voltage-
polarized directional element; see Figure 4.9) is the first priority directional
element to provide directional control for the neutral-ground and residual-
ground overcurrent elements.
If the negative-sequence voltage-polarized directional element is not operable
(i.e., it does not have sufficient operating quantity as indicated by its internal
enable, 32QGE, not being asserted; see Figure 4.6), then the second listed
directional element (V = zero-sequence voltage-polarized directional element;
see Figure 4.10) provides directional control for the neutral-ground and
residual-ground overcurrent elements.
If the zero-sequence voltage-polarized directional element is not operable
(i.e., it does not have sufficient operating quantity as indicated by its internal
enable, 32VE, not being asserted; see Figure 4.7), then the third listed
directional element (S = zero-sequence voltage-polarized directional element
[low-impedance]; see Figure 4.12) provides directional control for the neutral-
ground and residual-ground overcurrent elements.
If the zero-sequence voltage-polarized directional element (low-impedance) is
not operable (i.e., it does not have sufficient operating quantity as indicated by
its internal enable, 32NE [low-impedance], not being asserted; see
Figure 4.8), then no directional control is available. The neutral-ground and
residual-ground overcurrent elements will not operate, even though these
elements are designated with the DIRn (n = 1–4) settings to be directionally
controlled (see Figure 4.17 and Figure 4.18).
Another example, if setting:
ORDER = V
then the zero-sequence voltage-polarized directional element (V = zero-
sequence voltage-polarized directional element; see Figure 4.10) provides
directional control for the neutral-ground and residual-ground overcurrent
Courtesy of NationalSwitchgear.com
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