Schweitzer Engineering Laboratories SEL-351 - Internal Enables; Best Choice Ground Directional Logic; Directional Elements

Date Code 20001006 Loss-of-Potential, Load Encroachment, and Directional Element Logic 4-9
SEL-351 Instruction Manual
Thus, the zero-sequence voltage-polarized directional element in Figure 4.9 is defeated,
nonoperational, and unavailable when the voltage inputs are delta-connected (see Figures
1.2 and 1.3).
Internal Enables
Refer to Figure 4.4, Figure 4.5, and Figure 4.6.
The internal enables 32QGE, 32VE, and 32IE have the following correspondence to the directional
elements:
32QGE Negative-sequence voltage-polarized directional element
32VE Zero-sequence voltage-polarized directional element
32IE Channel IN current-polarized directional element
Note that Figure 4.5 has extra internal enable 32QE, which is used in the directional element logic
that controls negative-sequence and phase overcurrent elements (see Figure 4.13).
The settings involved with internal enables 32QGE, 32VE, and 32IE in Figure 4.5 and Figure 4.6
(e.g., settings a2, k2, a0) are explained in the following subsection Directional Control Settings.
Best Choice Ground Directional Logic
Refer to Figure 4.4 and Figure 4.7.
The internal enables 32QGE, 32VE, and 32IE and setting ORDER are used in the Best Choice
Ground Directional logic in Figure 4.7. The Best Choice Ground Directional logic determines
which directional element should be enabled to operate. The neutral ground and residual ground
overcurrent elements set for directional control are then controlled by this enabled directional
element.
Directional Elements
Refer to Figure 4.4, Figure 4.8, Figure 4.9, and Figure 4.10.
The enable output of Best Choice Ground Directional logic in Figure 4.7 determines which
directional element will run.
Additionally, note 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 zero-sequence voltage-
polarized directional elements are disabled (see Figure 4.8 and Figure 4.9).
The channel IN current-polarized directional element does not use voltage in making direction
decisions, thus a loss-of-potential condition does not disable the element, but rather aids in enabling
it. When the internal enable 32IE is asserted, the channel IN current-polarized directional element
(Figure 4.10) is enabled if enable setting ELOP = Y or Y1 and a loss-of-potential condition occurs
(Relay Word bit LOP asserts).
Refer to Figure 4.1 and accompanying text for more information on loss-of-potential.
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