Alstom MiCOM P54 Series, Техническое руководство, Страница: 220 / 1024

P54x/EN OP/La4 Operation
(OP) 5-46
MiCOM P543, P544, P545 & P546
OP
1.19.2 Actions upon power swing detection (Distance option only)
Once a power swing is detected the following actions occur:

Distance elements are blocked on selected zones providing blocking is enabled

All zones are switched to self polarized mho characteristics for maximum stability during
the swing

A power swing block alarm is issued when the swing impedance enters a distance zone.
The condition of entering an impedance zone avoids alarming for low current momentary
swings that settle quickly

When a power swing is in progress, the minimum threshold used by the phase selector
is increased to twice the maximum superimposed current prevailing in the swing
Therefore, the phase selector resets once a power swing is detected. It can then be
used to detect a fault during a power swing.
1.19.3 Detection of a fault during a power swing (Distance option only)
A fault is detected during a swing when the phase selector operates, based on its increased
threshold. Therefore, any operation of the phase selector will cause PSB unblocking, and
allow a trip. Example scenarios are:

A fault causes the delta current measured to increase above twice that stored during the
swing (a step change in delta I rather than the expected gradual transition in a power
swing).
1.19.4 Actions upon detection of a fault during a power swing (Distance option only)

The block signal is only removed from zones that start within 2 cycles of a fault being
detected. This improves stability for external faults during power swings. Any
measuring zone that was detecting an impedance within its characteristic before The
phase selector detected the fault will remain blocked. This minimizes the risk of tripping
for a swing impedance that may naturally be passing through Zone 1, and could
otherwise cause a spurious trip if all zones were unblocked on fault inception. Any
measuring zone that picks up beyond the two cycle window will remain blocked. This
minimizes the risk of tripping for a continued swing that may pass through Zone 1, and
could otherwise cause a spurious trip if all zones were allowed to unblock together.
1.19.5 Power swing settings (Distance option only)
The power swing detection is setting free aided with slow swing detection that uses zone 5
and does not require any system study. The only setting available to a user, apart from zone
5, is to decide whether a zone should be blocked or allowed to trip after a power swing is
detected. Zone by zone, it is possible to select one mode from the following:

“Allow Trip” - should a power swing locus remain within a trip zone
characteristic for a duration equal to the zone time
delay, the trip will be allowed to happen;

“Blocking” - to keep stability for that zone, even if a power swing
locus should enter it;

“Delayed Unblock” - maintains the block for a set duration. If the swing is
still present after the “PSB Timeout Set” window has
expired, tripping is allowed as normal.