Schweitzer Engineering Laboratories SEL-421-4 - Figure 6.33 OST Characteristics

6.131
Date Code 20171021 Instruction Manual SEL-421 Relay
Protection Applications Examples
Out-of-Step Logic Application Examples
NOTE: This setting philosophy
provides the most time for the relay to
decide whether the power swing is
unstable.
To configure the OOS logic for out-of-step tripping, enable the OOS logic. Next,
calculate the impedance reach settings for Zone 6 and Zone 7 (R1R6, R1R7,
X1T6, and X1T7), and then calculate OSTD (out-of-step trip delay) and OSBD
(out-of-step block time delay). All of the OOS settings appear in Table 6.37 and
Table 6.38.
Enable OOS Logic
Access Group settings to enable the out-of-step logic.
EOOS := Y. Out-of-Step (Y, N)
NOTE: Table 6.36 lists the settings
that the relay automatically calculates
and hides when you set EADVS to N.
You do not need to enable the Advanced Settings for this application example.
EADVS := N. Advanced Settings (Y, N)
Out-of-Step Tripping
When the positive-sequence impedance locus enters Zone 7, both OOS logic tim-
ers (OSBD and OSTD) start (see Figure 6.33). If OSTD expires before OSBD
and Zone 6 asserts, the relay declares an out-of-step tripping condition. Enable
the relay to trip when Zone 6 drops out (Trip-On-the-Way-Out). See Out-of-Step
Tripping and Blocking on page 6.133 for OSTD and OSBD calculations.
EOOST := O. Out-of-Step Tripping (N, I, O)
Figure 6.33 OST Characteristics
B
A
M
inimum Load
Im
p
edanc
e
Z
1
R1
X1
O
Ang_R6
6
Z
o
n
e
6
Z
o
n
e
2
Z
o
n
e
7
Ang_R7
T
O
W
I
T
O
W
O
where:
I = Enable out-of-step tripping (Trip-On-the-Way-In)
O = Enable out-of-step tripping (Trip-On-the-Way-Out)
N = Disable out-of-step tripping