ABB Relion 670 Series Technical Reference Manual page 270

Section 6
Impedance protection
264
RFPG R1+Rn
X1+Xn
RFPG
RFPG R1+Rn
ANSI05000661 V3 EN
Figure 132: Characteristic for the phase-to-ground measuring loops, ohm/loop
domain.
The fault loop reach may also be presented as in figure 133.
IA
VA
Phase-to-ground
fault in phase A
0
IN
ANSI06000412 V1 EN
Figure 133: Fault loop model
X
(Ohm/loop)
RFPG
Xn
Rn
j j
n n
R
RFPG
X1+Xn
RFPG
ANSI05000661-3-en.vsd
R1 + j X1
(Arc + tower
resistance)
(R0-R1)/3 +
j (X0-X1)/3 )
1MRK505222-UUS C
X0-X1
=
3
R0-R1
=
3
(Ohm/loop)
Phase-to-ground
element
RFPG
en06000412_ansi.vsd
Technical reference manual