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Instruction manual
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AQ G3x7 Generator protection IED
122 (211
)
Detection of “L1N”, “L2N”, “L3N” faults
Figure below explains the detection of a phase-to-ground
fault in phase “L1”:
o
No fault is detected in the previous sequential tests,
o
Start of the impedance logic loop “L1N”
o
The minimal impedance is measured in loop “L1N”
o
No start of the logic in another phase-to-ground loop,
o
The zero sequence current above the limit
o
The current in the phase involved is above the setting limit
o
The minimal impedance of the phase-to-ground loop is less than the minimal
impedance in the phase-to-phase loops.
In the figure below:
minLN = Minimum(ZL1N, ZL2N, ZL3N)
Figure 3-72: L1N fault detection
Figure 3-73:
L2N fault detection in Zone “n” (n=1...5)