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6.120
SEL-421 Relay
Instruction Manual
Date Code 20171021
Protection Applications Examples
Out-of-Step Logic Application Examples
Power System Parameters
lists the power system parameters.
Out-of-Step Blocking
This example demonstrates setting OSB function. Use this logic to discriminate
between power swings and faults to prevent unwanted distance element trips.
This application example assumes that you have set the phase-to-phase mho dis-
tance element Zone 2 reach. First, enable the OOS logic. Next, calculate the
impedance reach settings for Zone 6 and Zone 7 (R1R6, R1R7, X1T6, and
X1T7), and then calculate OSBD (out-of-step block time delay). All of the OOS
settings appear in
and
at the end of this example.
Enable OOS Logic
NOTE:
The relay automatically
calculates and hides settings when
you set EADVS to N and EOOST to N.
lists these settings.
Access Group settings to enable the out-of-step logic.
EOOS :=
Y
.
Out-of-Step (Y, N)
You do not need to enable the Advanced Settings for this application example.
EADVS :=
N
.
Advanced Settings (Y, N)
Out-of-Step Tripping
Disable the OST logic for this particular application example.
EOOST :=
N
.
Out-of-Step Tripping (N, I, O)
Phase-Distance Element Blocking
OSB logic blocks phase-distance protection during a swing when the measured
positive-sequence impedance enters the operating characteristics of the phase-
distance elements (see Zone 1 and Zone 2 in
). In practice, it is not
necessary to block all zones. In this application example, the OSB logic blocks
zones that generate instantaneous tripping. The OSB logic blocks instantaneous
Zone 1 and Zone 2 (Zone 2 is part of the communications-assisted tripping
scheme).
Table 6.32
Positive-Sequence Impedances (Secondary)
Parameter
Value
Line impedances:
Z
1L1
8.00
87.6° secondary (Z1MAG W ÐZ1ANG°)
Zone 2 Phase-Distance Reach:
Z
2MP
9.60
secondary
Source S impedances:
Z
1S
8.8
88° secondary
Source R impedances:
Z
1R
3.52
88° secondary
Nominal frequency (f
NOM
)
60 Hz
Nominal current (I
NOM
)
5 A secondary
Line Length
100 miles
Summary of Contents for SEL-421-4
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