4.32
SEL-351A Relay Instruction Manual Date Code 20080213
Loss-of-Potential, Load Encroachment, and Directional Element Logic
Directional Control for Negative-Sequence and Phase Overcurrent Elements (Not in SEL-351A-1)
Refer to Figure 4.1 and accompanying text for more information on loss-of-
potential.
Direction Forward/
Reverse Logic
Refer to Figure 4.19, Figure 4.23, and Figure 4.24.
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 4.4 shows the overcurrent elements that are controlled by each level
direction setting. Note in Table 4.4 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:
➤ 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 4.23 and
Figure 4.24 assert to logical 1. The referenced Level 1 overcurrent elements in
Figure 4.23 and Figure 4.24 are then not controlled by the directional control
logic.
If group setting VNOM = OFF, then the directional control outputs in
Figure 4.23 and Figure 4.24 assert to logical 1. This effectively makes the
phase and negative-sequence elements nondirectional.
See the beginning of Directional Control Settings (Not in SEL-351A-1) on
page 4.38 for a discussion of the operation of level direction settings DIR1–
DIR4 when the directional control enable setting E32 is set to E32 = N.
In some applications, level direction settings DIR1–DIR4 are not flexible
enough in assigning the desired direction for certain overcurrent elements.
Directional Control Provided by Torque Control Settings (Not in SEL-351A-1)
on page 4.57 describes how to avoid this limitation for special cases.
Courtesy of NationalSwitchgear.com
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