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6.130
SEL-421 Relay
Instruction Manual
Date Code 20171021
Protection Applications Examples
Out-of-Step Logic Application Examples
Out-of-Step Tripping
This example demonstrates how to set the OST (out-of-step tripping) function.
Use OST logic to detect an unstable power swing and trip the local terminal.
With OST logic, you can split the power system at predetermined locations after
an OST condition occurs.
The Zone 6 and Zone 7 settings for the OST logic depend on the positive
sequence impedance (Z
1
) trajectory of the power swing (see
). Set
inner Zone 6 at the point along the trajectory where the power system cannot
regain stability. Set Zone 7 so that the impedance because of maximum load con-
ditions is outside the Zone 7 characteristic for all loading conditions.
Table 6.35
Out-of-Step Tripping/Blocking
Setting
Prompt
Entry
OOSB1
Block Zone 1 (Y, N)
Y
OOSB2
Block Zone 2 (Y, N)
Y
OOSB3
Block Zone 3 (Y, N)
N
OSBD
Out-of-Step Block Time Delay (0.500–8000 cycles)
1.875
OSBLTCH Latch Out-of-Step Blocking (Y, N)
Y
EOOST
Out-of-Step Tripping (N, I, O)
N
X1T7
Zone 7 Reactance—Top (0.05 to 140
secondary)
21.29
X1T6
Zone 6 Reactance—Top (0.05 to 140
secondary)
11.52
R1R7
Zone 7 Resistance—Right (0.05 to 140
secondary)
15.53
R1R6
Zone 6 Resistance—Right (0.05 to 140
secondary)
5.77
X1B7
Zone 7 Reactance—Bottom (–0.05 to –140
secondary)
–21.29
X1B6
Zone 6 Reactance—Bottom (–0.05 to –140
secondary)
–11.52
R1L7
Zone 7 Resistance—Left (–0.05 to –140
secondary)
–15.53
R1L6
Zone 6 Resistance—Left (–0.05 to –140
secondary)
–5.77
50ABCP
Positive-Sequence Current Supervision (1.00–100 A secondary)
1.00
50QUBP
Negative-Sequence Current Supervision (OFF, 0.50–100 A secondary) OFF
UBD
Negative-Sequence Current Unblock Delay (0.500–120 cycles)
0.500
UBOSBF
Out-of-Step Angle Unblock Rate (1–10)
4
50Q1P
Level Pickup (OFF, 0.25–100 Amps sec.)
OFF
67Q1D
Level 1 Time Delay (0.000–16000 cycles)
0.000
67Q1TC
Level 1 Torque Control (SEL
OGIC
Equation)
1
Summary of Contents for SEL-421-4
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