Schweitzer Engineering SEL-351P, Quick Start Manual

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4-2 Loss-of-Potential, Load Encroachment, and Directional Element Logic Date Code 990430
SEL-351P Manual Técnico
The loss-of-potential enable setting, ELOP, does not enable or disable the LOP logic. It just
routes the LOP Relay Word bit to different logic, as is shown in Figure SECTION 4: .1 and
explained in the remainder of this subsection.
Setting ELOP = Y or Y1
If setting ELOP = Y or Y1 and a loss-of-potential condition occurs (Relay Word bit LOP asserts
to logical 1), negative-sequence voltage-polarized, zero-sequence voltage-polarized, and positive-
sequence voltage-polarized directional elements are disabled (see Figure SECTION 4: .9,
Figure SECTION 4: .10, Figure SECTION 4: .11, Figure SECTION 4: .17 and
Figure SECTION 4: .18). The loss-of-potential condition makes these voltage-polarized
directional elements unreliable. Thus, they are disabled. The overcurrent elements controlled by
these voltage-polarized directional elements are also disabled (unless overridden by conditions
explained in the following Setting ELOP = Y discussion).
In Figure 5.6, if setting ELOP = Y1 and LOP asserts, keying and echo keying in the permissive
overreaching transfer trip (POTT) logic are blocked.
Setting ELOP = Y
Additionally, if setting ELOP = Y and a loss-of-potential condition occurs (Relay Word bit LOP
asserts to logical 1), overcurrent elements set direction forward are enabled (see
Figure SECTION 4: .12, Figure SECTION 4: .13, and Figure SECTION 4: .19). These
direction forward overcurrent elements effectively become nondirectional and provide
overcurrent protection during a loss-of-potential condition.
As detailed previously, voltage-based directional elements are disabled during a loss-of-potential
condition. Thus, the overcurrent elements controlled by these voltage-based directional elements
are also disabled. But this disable condition is overridden for the overcurrent elements set
direction forward if setting ELOP = Y.
Setting ELOP = N
If setting ELOP = N, the loss-of-potential logic still operates (Relay Word bit LOP asserts to
logical 1 for a loss-of-potential condition) but does not disable any voltage-based directional
elements (as occurs with ELOP = Y or Y1) or enable overcurrent elements set direction forward
(as occurs with ELOP = Y).