Schweitzer Engineering SEL-351P, Quick Start Manual

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4-10 Loss-of-Potential, Load Encroachment, and Directional Element Logic Date Code 990430
SEL-351P Manual Técnico
Neutral ground overcurrent directional logic, shown in Figure SECTION 4: .13, uses the
quantities listed above along with zero-sequence polarized, neutral-current directional element
outputs from Figure SECTION 4: .11.
Loss-of-Potential
Note that 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 point (Relay Word bit 32GF) asserts to logical 1, thus enabling the neutral
ground and residual ground 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: .9, Figure SECTION 4: .10, and
Figure SECTION 4: .11), voltage-based directional elements are disabled during a loss-of-
potential condition. Thus, the overcurrent elements controlled by these voltage-based directional
elements are disabled also. 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.
Direction Forward/Reverse Logic
Refer to Figure SECTION 4: .4, Figure SECTION 4: .14, and Figure SECTION 4: .15.
The forward (Relay Word bits 32GF and 32NF) and reverse (Relay Word bits 32GR and 32NR)
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 output in Figure SECTION 4: .14 asserts to
logical 1. The Level 1 overcurrent elements referenced in Figure SECTION 4: .14 and
Figure SECTION 4: .15 are then not controlled by the directional control logic.