Schweitzer Engineering SEL-351P, Quick Start Manual

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4-22 Loss-of-Potential, Load Encroachment, and Directional Element Logic Date Code 990430
SEL-351P Manual Técnico
Direction Forward/Reverse Logic
Refer to Figure SECTION 4: .16, Figure SECTION 4: .20, and Figure SECTION 4: .21.
The forward (Relay Word bits 32QF and 32PF) and reverse (Relay Word bits 32QR and 32PR)
logic points are routed to the different levels of overcurrent protection by the level direction
settings DIR1 through DIR4.
Table SECTION 4: .1 shows the overcurrent elements that are controlled by each level direction
setting. Note in Table SECTION 4: .1 that all the time-overcurrent elements (51_T elements)
are controlled by the DIR1 level direction setting.
In most communications-assisted trip schemes, the levels are set as follows (see Figure 5.4):
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)
If a level direction setting (e.g., DIR1) is set:
DIR1 = N (nondirectional)
then the corresponding Level 1 directional control outputs in Figure SECTION 4: .20 and
Figure SECTION 4: .21 assert to logical 1. The referenced Level 1 overcurrent elements in
Figure SECTION 4: .20 and Figure SECTION 4: .21 are then not controlled by the directional
control logic.
See the beginning of following subsection Directional Control Settings for discussion of the
operation of level direction settings DIR1 through DIR4 when the directional control enable
setting E32 is set to E32 = N.
In some applications, level direction settings DIR1 through DIR4 are not flexible enough in
assigning the desired direction for certain overcurrent elements. Subsection
Directional Control
Provided by Torque Control Settings at the end of this section describes how to avoid this
limitation for special cases.