• A fault occurs on a so far healthy power line, over which the power swing has
been detected and the fast distance protection zone has been blocked by ZMRPSB
(68) element.
• The power swing occurs over two phases of a protected line during the dead time
of a singlepole auto-reclosing after the Ph-E fault has been correctly cleared by the
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
230) causes the
measured impedance to enter the operate area of ZMRPSB (68) function and, for
example, the zone 2 operating characteristic (see figure 231). 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 231.
E
A
A
B
C
D
F
Z
SA
RA
E
C
E
D
xx06000238.vsd
Z
SC
Z
SD
IEC06000238 V1 EN-US
Figure 230: 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 504 163-UUS A Section 8
Impedance protection
Transformer protection RET670 2.2 ANSI 459
Application manual
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