Schweitzer Engineering Laboratories SEL-421-4, Instruction Manual

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5.51
Date Code 20171021 Instruction Manual SEL-421 Relay
Protection Functions
Out-of-Step Logic (Conventional)
(i.e., an unbalanced fault has occurred). The negative-sequence current level
detector 50QUB determines the sensitivity of the 67QUBF or 67QUBR elements,
for all zones except Zone 1.
If a three-phase fault occurs during a power swing that has operated the OOS
logic, the logic also overrides OOS blocking; a set of internally derived inner
blinders encompasses the protected line and detects internal three-phase faults.
The OOS logic can also detect a power swing when a single-pole open condition
exists; for such a case, the logic can block both phase and ground-distance pro-
tection.
Refer to Section 6: Protection Applications Examples for detailed descriptions of
the various functions utilized by the OOS logic.
The following rules apply when you set the OOS logic:
➤
You can enable the OOS logic when setting Z1ANG is greater than
45 degrees.
➤
Settings X1T6, X1T7, R1R6, and R1R7 must be set to a positive
value.
➤
Settings X1B6, X1B7, R1L6, and R1L7 must be set to a negative
value.
➤
Setting R1R6 must be set less than R1R7.
Figure 5.32 OOS Characteristics
Zone 2
Zone 6
Zone 7
Zone 3
Zone 1
Right
Inner-Blinder
Left
Inner-Blinder
Z1L1
(R1L6)
(R1L7)
(R1LB)
(R1RB)
(R1R6)
R1
X1
(X1T7)
(R1R7)
Z1
Trajectory
(X1B7)
(X1B6)
(X1T6)