Instruction manual
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AQ F3x0 Feeder protection IED
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Calculation method Calc(E):
The currents are suitable but the voltages are in the range of the CVT swings, there are no
pre-fault voltages stored in the memory but because of asymmetrical faults, there are
healthy phase voltages. Therefore, during the first 35 ms the directional decision is based
on healthy voltages
R, X=f(u, i) direction = f(Uhealthy, i) /in the first 35 ms/
R, X=f(u, i) direction = f(u, i) /after 35 ms/
This directional decision is based on a special voltage compensation method (Bresler). The
product of the Fourier components of the phase currents and the highest zone impedance
setting value is composed. These compensated voltage values are first subtracted from the
corresponding phase voltages. If the phase sequence of theses resulting voltages is (L1,L3,
L2), the fault is in the forward direction. The reverse direction is decided based on the
compensated voltages added to the corresponding phase voltages. If this resulting phase
sequence is (L1,L3, L2), the fault is in the backward direction. If both phase sequences are
(L1, L2, L3), the direction of the fault is undefined.
Calculation method Calc(F):
The currents are suitable but the voltages are too low, there are no pre-fault voltages stored
in the memory but because of asymmetrical faults, there are healthy voltages. Therefore,
the directional decision is based on healthy voltages
R, X=f(u, i) direction = f(Uhealthy, i)
The directional decision is described in calculation method Calc(E).
Calculation method Calc(G):
If no directional decision is required, then the decision is based on the absolute value of the
impedance (forward fault is supposed)
R=abs(R), X=abs(X)
Calculation method Calc(H):
If the voltage is not sufficient for a directional decision and no stored voltage samples are
available, then the impedance is set to a high value:
