R.1.44
SEL-421 Relay Reference Manual Date Code 20111215
Protection Functions
Out-of-Step Logic
Figure 1.30 OOS Characteristics
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 protection.
Refer to Section 1: Protection Application Examples in the Applications
Handbook 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.
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)
Z
1
Trajectory
(X1B7)
(X1B6)
(X1T6)
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