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 Figure 6.33). 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
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