distance protection. The second fault can, but does not need to, occur within this time
interval.
• Fault on an adjacent line (behind the B substation, see figure 228) causes the
measured impedance to enter the operate area of ZMRPSB (68) function and, for
example, the zone 2 operating characteristic (see figure
229). Correct fault clearance
initiates an evolving power swing so that the locus of the measured impedance
continues through zone 1 operating characteristic and causes its unwanted operation,
if no preventive measures have been taken, see figure
229.
E
A
A
B
C
D
F
Z
SA
RA
E
C
E
D
xx06000238.vsd
Z
SC
Z
SD
IEC06000238 V1 EN
Figure 228: Fault on adjacent line and its clearance causes power swinging between
sources A and C
PSLPSCH function and the basic operating principle of ZMRPSB (68) function operate
reliably for different faults on parallel power lines with detected power swings. It is,
however, preferred to keep the distance protection function blocked in cases of single
phase-to-ground faults on so far healthy lines with detected power swings. In these cases,
it is recommended to use an optionally available directional overcurrent ground-fault
protection with scheme communication logic.
1MRK 506 369-UUS - Section 8
Impedance protection
Line distance protection REL670 2.2 ANSI 445
Application manual
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