Instruction manual
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AQ G3x7 Generator protection IED
104 (211
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3.2.21.2
Principle of the impedance calculation
The impedance protection continuously measures the impedances in the six possible fault
loops. The calculation is performed in the phase-to-phase loops based on the line-to-line
voltages and the difference of the affected phase currents, while in the phase-to-earth loops
the phase voltage is divided by the phase current compounded with the zero sequence
current. These equations are summarized in table below for different types of faults. The
result of this calculation is the positive sequence impedance of the fault loop, including the
positive sequence fault resistance at the fault location.
Table 3-40: Impedance calculation formulas
The central column contains the formula for calculation. The formulas referred to in the right-
hand-side column yield the same impedance value.
Equation 3-4: Earth fault compensation factor