P.3.173
Date Code 20151029 Protection Manual SEL-411L Relay
Protection Functions
Out-of-Step Logic (Zero Settings)
Figure 3.113 shows the I0/I2 angular relationship during a single pole open
condition, and no system fault present. Figure 3.114 shows the blocking
principle of the A-phase-to-ground mho element by the deasserted OSBA
signal.
Figure 3.113 I0/IA2 Angle Supervision During Pole-Open Situation
Figure 3.114 Blocking of the MAG Signal by the OSBA Fault Detection
The same principle applies to OSBB and OSBC. When all three poles are
closed, OSBA, OSBB, and OSBC are deasserted and the distance elements
can trip normally, even during a power swing.
In Figure 3.112, the logic is enabled when the zero-sequence supervisory
directional overcurrent element (50GR or 50GF) and negative-sequence
supervisory directional overcurrent element (50QR or 50QF) pick up during a
single pole open condition (SPO). Table 3.89 shows the input/output
combinations of the logic.
Phase Mho Element
Reset Logic
If the OSB function is enabled and a power swing occurs, the OSB signal
blocks the phase-fault detectors, but not the ground-fault detectors. Therefore,
in order to remove the OSB signal and clear a fault that occurs during an OOS
condition, the relay must detect three-phase and phase-to-phase faults (see
Figure 3.115).
Figure 3.115 Unblocking of the MAB Signal by the 67QUB Element
Table 3.89 Input/Output Combinations of the Pole-Open OOS Blocking Logic
Gate Turned On Open Phase Phases to Block
AND 6 A-phase Phases B and C
AND 7 B-phase Phases A and C
AND 8 C-phase Phases C and A
A-Phase open
Normal IO/IA2 angle location
B-Phase
Normal IO/IA2 angle location
C-Phase open
Normal IO/IA2 angle location
MAG
Phase A-G
mho signal
OSB
OSBA
Ground A-to-G
distance logic
MAB
Phases A-B
mho signal
OSB
67QUB
Phase A-to-B
distance logic
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