2.3 Power swing detection (optional)
109
7SA522 Manual
C53000-G1176-C155-3
the event of a short-circuit (1), the impedance vector abruptly changes from the load
condition into this fault detection range. However, in the event of a power swing, the
apparent impedance vector initially enters the power swing range PPOL and only later
enters the fault detection range APOL (2). It is also possible that a power swing vector
will enter the area of the power swing range and leave it again without coming into
contact with the fault detection range (3). If the vector enters the power swing polygon
and passes through it leaving on the opposite side, then the sections of the network
seen from the relay location have lost synchronism (4): The power transfer is unstable.
Figure 2-36 Pickup characteristic of the power swing detection for a polygon.
The same applies to the MHO circle characteristic (refer to Figure 2-37). The power
swing circle also has a distance Z
Diff
of 5 Ω (at I
N
= 1 A) or 1 Ω (at I
N
= 5 A) from the
largest zone circle. If one or more reverse zones are set, this impedance distance from
all zones is maintained.
The rate of change of the 3 impedance vectors is monitored in
1
/
4
cycle intervals.
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