Sel SEL-421 - Out-Of-Step Logic; Load-Encroachment Logic Relay Settings; Load-Encroachment Logic Relay Word Bits

R.1.43
Date Code 20111215 Reference Manual SEL-421 Relay
Protection Functions
Out-of-Step Logic
Out-of-Step Logic
The out-of-step (OOS) logic determines whether a power swing is stable. This
relay logic can be set to either block distance protection or allow tripping
when the measured positive-sequence impedance (Z
1
) remains between inner
Zone 6 and outer Zone 7 longer than either the OOS blocking delay (setting
OSBD) or the OOS tripping delay (setting OSTD), respectively (refer to
Figure 1.30).
NOTE: E50Q must be set to 1 or
greater for enabling 67Q1T override of
OOS blocking for Zone 1 (see
Figure 1.35, Figure 1.38, and
Figure 1.41).
The OOS logic detects all power swings that enter the OOS characteristics,
even if a single-pole open condition exists (Relay Word bit SPO equals
logical 1). If either negative-sequence directional element 67QUBF or
67QUBR (67Q1T for Zone 1) picks up during a power swing and a single-
pole open condition does not exist (Relay Word bit SPO equals logical 0), the
logic overrides OOS blocking (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.
Table 1.38 Load-Encroachment Logic Relay Settings
Name Description Range
Default
(5 A)
ELOAD Load Encroachment Y, N Y
ZLF Forward Load Impedance () (0.25–320)/I
nom
9.22
ZLR Reverse Load Impedance () (0.25–320)/I
nom
9.22
PLAF Forward Load Positive Angle () –90.0 to +90 30.0
NLAF Forward Load Negative Angle () –90.0 to +90 –30.0
PLAR Reverse Load Positive Angle () 90.0–270 150.0
NLAR Reverse Load Negative Angle () 90.0–270 210.0
Table 1.39 Load-Encroachment Logic Relay Word Bits
Name Description
ZLOAD ZLIN OR ZLOUT
ZLIN Import load impedance detected
ZLOUT Export load impedance detected