Schweitzer Engineering SEL-351P - Directional Elements; Directional Element Routing; Loss-Of-Potential

Date Code 990430 Loss-of-Potential, Load Encroachment, and Directional Element Logic 4-21
SEL-351P Manual Técnico
Directional Elements
Refer to
Figure SECTION 4: .16, Figure SECTION 4: .17, and Figure SECTION 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 SECTION 4: .17 and Figure SECTION 4: .18).
Refer to
Figure SECTION 4: .1 and accompanying text for more information on loss-of-
potential.
Note in
Figure SECTION 4: .16 and Figure SECTION 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 unbalanced faults while the positive-sequence
voltage-polarized directional element operates for three-phase faults.
Note also in
Figure SECTION 4: .18 that the assertion of ZLOAD disables the positive-sequence
voltage-polarized directional element. ZLOAD asserts when the relay is operating in a user-
defined load region (see
Figure SECTION 4: .2).
Directional Element Routing
Refer to
Figure SECTION 4: .16 and Figure SECTION 4: .19.
The directional element outputs are routed to the forward (Relay Word bits 32QF and 32PF) and
reverse (Relay Word bits 32QR and 32PR) logic points and then on to the direction
forward/reverse logic in
Figure SECTION 4: .20 and Figure SECTION 4: .21.
Loss-of-Potential
Note if both
the following are true:
• Enable setting ELOP = Y,
• A loss-of-potential condition occurs (Relay Word bit LOP asserts),
then the forward logic points (Relay Word bits 32QF and 32PF) assert to logical 1, thus, enabling
the negative-sequence and phase overcurrent elements that are set direction forward (with
settings DIR1 = F, DIR2 = F, etc.). These direction forward overcurrent elements effectively
become nondirectional and provide overcurrent protection during a loss-of-potential condition.
As detailed previously (in
Figure SECTION 4: .17 and Figure SECTION 4: .18), 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.
Refer to
Figure SECTION 4: .1 and accompanying text for more information on loss-of-
potential.