ABB Relion 670 series, Technical Reference Manual

Page: 187 / 1232

Here IN is a phasor of the residual current in IED point. This results in the same reach
along the line for all types of faults.
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 (
D
I ) 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 ,
D
= × + ×
w D
0
X i
V R i
t
EQUATION1547 V1 EN
(Equation 6)
in complex notation, or:
0
Re ( )
Re ( ) Re ( )
X I
V R I
t
D
= × + ×
w D
EQUATION1548 V1 EN
(Equation 7)
0
Im ( )
Im ( ) Im ( )
X I
V R I
t
D
= × + ×
w D
EQUATION1549 V1 EN
(Equation 8)
with
1MRK505222-UUS C
Section 6
Impedance protection
181
Technical reference manual