The apparent impedance is considered as an impedance loop with resistance R and
reactance X.
The formula given in equation 5 is only valid for radial feeder application without load.
When load is considered in the case of single phase-to-ground fault, conventional
distance protection might overreach at exporting end and underreach at importing end.
The IED has an adaptive load compensation which increases the security in such
applications.
Measuring elements receive current and voltage information from the A/D converter.
The check sums are calculated and compared, and the information is distributed into
memory locations. For each of the six supervised fault loops, sampled values of
voltage (V), current (I), and changes in current between samples (DI) are brought from
the input memory and fed to a recursive Fourier filter.
The filter provides two orthogonal values for each input. These values are related to the
loop impedance according to equation
6,
EQUATION1547 V1 EN (Equation 56)
in complex notation, or:
0
Re ( )
Re ( ) Re ( )
X I
V R I
t
D
= × + ×
w D
EQUATION1548 V1 EN (Equation 57)
0
Im ( )
Im ( ) Im ( )
X I
V R I
t
D
= × + ×
w D
EQUATION1549 V1 EN (Equation 58)
with
EQUATION356 V1 EN (Equation 59)
where:
Re designates the real component of current and voltage,
Im designates the imaginary component of current and voltage and
f
0
designates the rated system frequency
Section 6 1MRK505222-UUS C
Impedance protection
312
Technical reference manual
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