
4-20
Loss-of-Potential, Load Encroachment, and Directional Element Logic
Date Code 20020215
SEL-351R Instruction Manual
Figure 4.16: General Logic Flow of Directional Control for Negative-Sequence and Phase
Overcurrent Elements
The negative-sequence voltage-polarized directional element has priority over the positive-
sequence voltage-polarized directional elements in controlling the phase overcurrent elements.
The negative-sequence voltage-polarized directional element operates for unbalanced faults,
while the positive-sequence voltage-polarized directional element operates for three-phase faults.
Internal Enables
Refer to Figure 4.5 and Figure 4.16.
The internal enable 32QE corresponds to the negative-sequence voltage-polarized directional
element.
Note that Figure 4.5 has extra internal enable 32QGE, which is used in the directional element
logic that controls the neutral ground and residual ground overcurrent elements (see Figure 4.4).
The settings involved with internal enable 32QE in Figure 4.5 (e.g., settings a2, k2) are explained
in a following subsection
Directional Elements
Refer to Figure 4.16, Figure 4.17, and Figure 4.18.
If enable setting ELOP = Y or Y1 and a loss-of-potential condition occurs (Relay Word bit LOP
asserts), the negative-sequence voltage-polarized and positive-sequence voltage-polarized
directional elements are disabled (see Figure 4.17 and Figure 4.18).
Refer to Figure 4.1 and accompanying text for more information on loss-of-potential.
Note in Figure 4.16 and Figure 4.18, that the assertion of internal enable 32QE (for the negative-
sequence voltage-polarized directional element) disables the positive-sequence voltage-polarized
directional element. The negative-sequence voltage-polarized directional element has priority
over the positive-sequence voltage-polarized directional elements in controlling the phase
overcurrent elements. The negative-sequence voltage-polarized directional element operates for
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