Siemens siprotec 7SA522 User Manual page 221

7SA522 Manual
C53000-G1176-C119-2
1 A) or 1 Ω (at I
= 5 A) in all directions from the fault detection range. In the event of
N
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 im-
pedance 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.
–R
P
Z
diff
Figure 6-41 Pick up characteristic of the power swing detection for a polygon.
The same applies to the MHO circle characteristic (refer to Figure 6-42). The power
swing circle also has a distance Z
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 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.
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
of 5 Ω (at I
diff
Line-
characteristic
PPOL
APOL
(4)
(3)
(2)
(1)
R R = R + Z
A P A
= 1 A) viz. 1 Ω (at I
N N
1
/ –period–cycles.
4
Functions
diff
R
= 5 A) from the
6-73