4.47
Date Code 20170927 Instruction Manual SEL-751 Relay
Protection and Logic Functions
Group Settings (SET Command)
q From Figure 4.33; w Figure 4.8; e Figure 4.2.
Figure 4.35 Direction Forward/Reverse Logic for Neutral Ground
Overcurrent Elements
Directional Control
for Negative-
Sequence and Phase
Overcurrent Elements
The directional control for overcurrent elements is enabled by making direc-
tional control enable setting EDIR. Setting EDIR and other directional control
settings are described in Directional Control Settings on page 4.53.
The negative-sequence voltage-polarized directional element controls the neg-
ative-sequence overcurrent elements. Negative-sequence voltage-polarized
and positive-sequence voltage-polarized directional elements control the
phase overcurrent elements. Figure 4.36 gives an overview of how the nega-
tive-sequence voltage-polarized and positive-sequence voltage-polarized
directional elements are enabled and routed to control the negative-sequence
and phase overcurrent elements.
If three-phase voltage signals are not available, make the setting VNOM =
OFF. If SINGLEV := Y, setting VNOM is set to OFF. This turns off the nega-
tive-sequence voltage-polarized and positive-sequence voltage-polarized ele-
ments to prevent them from operating on false voltage quantities, yet still
allows the Best-Choice Ground Directional Element logic, if available, to
operate for ground faults. This shut-down logic is shown in the center portions
of Figure 4.23 and Figure 4.38.
Level
Direction
Settings
Directional
Control
DIRNF
DIR1 = F
DIR1 = N
Relay
Word
Bits
to Neutral Ground
Time-0vercurrent
Elements
to Neutral Ground
Instantaneous/
Definite-Time
Overcurrent
Elements
ORDER = OFF
Setting
Forward
Forward
DIRNR
Reverse
Level 1
N1DIR
DIR1 = R
Reverse
DIR2 = F
DIR2 = N
Forward
Level 2
N2DIR
DIR2 = R
Reverse
DIR3 = F
DIR3 = N
Forward
Level 3
N3DIR
DIR3 = R
Reverse
DIR4 = F
DIR4 = N
Forward
Level 4
N4DIR
DIR4 = R
Reverse
1
1
2
3
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