ABB RELION 670 SERIES Applications Manual page 276

Section 8
Impedance protection
270
Case 2: Parallel line switched off and not earthed or earthed at one line end
ANSI13000256 V1 EN
Figure 132: Parallel line is out of service and not earthed
-
Z Z
0 1
+
1
3 Z
×
1
= ×
Z x Z
1
+
1 K
N
IECEQUATION14012 V1 EN
Case 3: Both lines in service
ANSI13000257 V1 EN
Figure 133: Class 1, parallel line in service
GUID-354B9143-D19E-4835-BCEA-737D7C5E02AA V1 EN
Some observations from above equations for case 1, 2, and 3
In case 1, the lowest impedance is measured, that is, the highest reach occurs due to the
parallel connection of the zero-sequence systems of both lines.
In case 3, the highest impedance is measured, which corresponds to the shortest reach.
x Ph-G
0m
1MRK 506 369-UUS -
(Equation 174)
ANSI13000257-1-en.vsd
(Equation 175)
Line distance protection REL670 2.2 ANSI
Application manual