Operation P54x/EN OP/La4
MiCOM P543, P544, P545 & P546
(OP) 5-45
OP
1.19 Power swing detection, alarming and blocking (Distance option only)
1.19.1 Detection of power swings (Distance option only)
A powe
r swing may cause the impedance presented to a distance relay to move away from
the normal load area and into one or more of its tripping characteristics. In the case of a
stable power swing it is important that the relay should not trip. The relay should also not trip
during loss of stability since there may be a utility strategy for controlled system break up
during such an event.
The power swing detection in the MiCOM P54x is an advanced technique that uses
superimposed current (I) detector similar to the phase selection principle described above.
However for the power swing detector the current is always compared to that 2 cycles
previous. For a fault condition this power swing detector (PSD) will reset after 2 cycles as no
superimposed current is detected.
For a power swing, PSD will measure superimposed current for longer than 2 cycles, and it
is the length of time for which the superimposed current persists that is used to distinguish
between a fault and a power swing. A power swing is deemed to be in progress if a three
phase selection, or a phase to phase selection when one pole is open, produced in this way
is retained for more than 3 cycles, as shown in Figure 25. At this point the required distance
zon
es can be blocked, to avoid tripping should the swing impedances cross into a tripping
zone.
Fault
Power
swing
3
cycles
PH1
PH2
PSB active
PSB removed
including
3 faults
Æ
& minimum
threshold
increased
P1181ENa
Figure 25 Power swing detected for 3 cycles continuous I (Distance option only)
In order to detect slow power swings, when the superimposed current remains below the
minimum threshold (5%In), a complementary method of detection could be used. This
method requires zone 5 to be set. For the zone 5 setting, no system study is required, it is
only necessary to set the R5 and R5’ reach below the minimum possible load impedance, as
explained in the Application Section. If the fault impedance remains within a zone 5 for at
least 1 cycle without phase selection operation, the slow swing is declared. This
complementary method works in parallel to the automatic, setting free technique explained
above.
Note: Zone 5 has a dual purpose: OST protection and slow swing detection.
There is no conflict in zone 5 settings, i.e. zone 5 settings for OST
protection (if applied) perfectly suit slow swing detection.
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