J. Jaeger et al.
R-X-impedance plane of the distance protection devices at line L_0255.
The trajectory of the impedance vector is crossing the zone 3 and the timer of zone 3 elapses before the tra-
jectory could leave the zone. Four time events T1, T2, T3 and T4 are marked in Figure 5 to describe the time-
line. At T1 the fault appears at line L_00256, T2 is the time after the selective trip in zone 1 of the protection
device located at the southern station. T3 is the moment after the trip in zone 2 of the other distance protection
of line L_00256. The last time T4 describes the mal-trip in zone 3 of the distance protection of line L_00255.
This trip provokes that the swing center moves into the 115 kV voltage level. Now the trajectory is crossing the
tripping zones of the distance protection devices of the lines L_00188 and L_00187 and both lines trip. Hence
the north/center grid is separated from the south grid. One possible countermeasure against this cascading fault
and the consequent major disturbance is shown in Figure 5(b). The introduction of blinders may avoid the un-
necessary tripping of L_00255 and the cascading fault is not taking its course.
4. Conclusions
New innovative strategies of protection security assessment are proposed. It could be shown that the protection
security can be improved using the SIGUARD®-PSA system. This can be applied to nationwide transmission
systems as well as space limited distribution systems. Different aspects can be checked using only one simula-
tion setup.
The proposed simulation method is able to identify critical contingencies with regard to short-circuit current
simulation as well as the dynamic protection behaviour. Many different influences on the dynamic protection
behaviour are given by the network and the protection system itself. The evaluation gives rather reliable results
based on real network data. The case study shows that it is important for the assessment of the dynamic behav-
iour to consider protection devices simultaneously because stable situations can be changed into unstable prob-
lems by protection responses. Major disturbances or blackouts are often activated by such problems and could
be identified and prevented by such a simulation. The analysis of these problems can also help to derive new
practical protection functions in order to avoid unnecessary power supply interruptions anticipatorily. This is
properly supporting the protection security assessment in today’s and future power grids.
References
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