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7SA6 Manual
C53000-G1176-C156-2
short-circuits will result in the fast cancellation of the power swing block in the affected
phases, thereby allowing the tripping of the Distance Protection.
To detect a power swing, the rate of change of the impedance vector is measured. The
measurement is started when the impedance vector enters the power swing measur-
ing range PPOL (refer to Figure 6-40). The fault detection range APOL is made up of
the largest set values for R and X of all the activated zones. The power swing zone
has a minimum distance Z
from the fault detection zone. In 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 vec-
tor 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.
–R
P
Z
Diff
Figure 6-40
Pick up characteristic of the power swing detection for a polygon.
The rate of change of the three impedance vectors is monitored in
If an impedance vectors, moving on a continuous curve, enters the power swing
measuring range PPOL, a power swing condition is assumed. If on the other hand an
impedance vector changes abruptly, this can only result from a load jump or short cir-
cuit.
of 5 Ω (at I
= 1 A) or 1 Ω (at I
diff
N
jX
X
= X
+ Z
P
A
Diff
power swing range
X
A
fault detection range
ϕ
–R
line
A
–X
A
Z
Diff
–X
P
Line-
characteristic
= 5 A) in all directions
N
Line-
characteristic
PPOL
APOL
(4)
(3)
(2)
(1)
R
R
= R
+ Z
A
P
A
1
/
–period–cycles.
4
Functions
Diff
R
6-73
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