4-20 Loss-of-Potential, Load Encroachment, and Directional Element Logic Date Code 20001006
SEL-351 Instruction Manual
Direction Forward/Reverse Logic
Refer to Figure 4.13, Figure 4.17, and Figure 4.18.
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 4.1 shows the overcurrent elements that are controlled by each level direction setting. Note
in Table 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 4.17 and Figure 4.18 assert to
logical 1. The referenced Level 1 overcurrent elements in Figure 4.17 and Figure 4.18 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.
Courtesy of NationalSwitchgear.com
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