Instruction manual
–
AQ G3x7 Generator protection IED
118 (211
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Table 3-50: Input signals for three phase start decision of the impedance protection function.
Table 3-51: Table 3-36: Inputs needed for three phase start decision
Detection of “L1L2”, “L2L3”, “L3L1” faults
Figure below explains the detection of a phase-to-
phase fault between phases “L1” and
“L2”:
o
no fault is detected in the previous sequential tests,
o
the start of the polygo
n impedance logic in loop “L1L2” detects the lowest
reactance and
o
“OR” relation of the following logic gates:
o
No zero sequence current above the limit and no start of the function in another
phase-to-phase loop, or
o
In the presence of a zero sequence current
▪
Start of the polygon impedance logic in loops “L1”
and “L2” individually as
well, or
▪
The voltage is small in the faulty “L1L2” loop and the currents in both phases
involved are above the setting limit.
The “L1L2” fault detection resets only if none of the “L1L2” line
-to-
line, “L1N” or “L2N” loops
detect fault any longer.
