Woodward
Manual XRI1-ER
16
TD_XRI1-ER_12.03, Rev. C
Figure 4.4: Phase position between the residual voltage and zero sequence current for faulted and non-faulted lines in
case of compensated systems (cos
φ)
U
E
- residual voltage
I
E
- zero sequence current
I
L
- inductive component of zero sequence current (caused by Petersen coil)
I
C
- capacitive component of zero sequence current
I
W
- resistive component of zero sequence current
In compensated mains the earth fault direction cannot be determined from the reactive current components be-
cause the reactive part of the earth current depends upon the compensation level of the mains. The ohmic
component of the total current (calculated by cos
φ adjustment) is used in order to determine the direction.
The resistive component in the non-faulted line is in phase with the residual voltage, while the resistive compo-
nent in the faulted line is opposite in phase with the residual voltage.
By means of an efficient digital filter harmonics and fault transients in the fault current are suppressed. Thus, the
uneven harmonics which, for instance, are caused an electric arc fault, do not impair the protective function.
