-1 -0.5 0 0.5 1 1.5
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Real part (R) of Z in Ohms
→
Imaginary part (X) of Z in Ohms
→
^
^ ^
^
^
^ ^
^
^
^
^ ^
^
^
^ ^
^
^
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
- -
-
-
-
-
-
-
-
-
-
-
-
-
-
- - -
-
-
-
-
-
-
-
-
-
-
-
-
-
-
G
relay
relay
fault
RE
X [Ohm]
SE
X-line
→
limit of
reach
zone 2
zone 1
Z(R,X) 20 ms
after line out
this circle forms
the right-hand side
edge of the lens
0
6
pre-fault
Z(R,X)
5
1
2
3
4
0
→
pre-fault Z(R, X)
3
→
Z(R, X) under fault
5
→
Z 20 ms after line out
6
→
pow er line reclosed
R
SE RE
lens
→
110°
Z-line
→
fault
→
ANSI10000111-1-en.vsd
ANSI10000111 V1 EN-US
Figure 202: A stable case where the disturbance does not make the generator to go out-of-
step
It shall be observed that for a stable case, as shown in Figure 202, where the disturbance does not
cause the generator to lose step, the complex impedance Z(R, X) exits the lens characteristic on
the same side (point 4) it entered it (point 2), and never re-enters the lens. In a stable case, where
the protected generator remains in synchronism, the complex impedance returns to quadrant 1,
and, after the oscillations fade, it returns to the initial normal load position (point 0), or near.
7.11.7.1 Lens characteristic
GUID-F9BD3225-C87F-4FA6-A267-2248F0A4E707 v6
A precondition in order to be able to construct a suitable lens characteristic is that the power
system in which OOSPPAM (78) is installed, is modeled as a two-machine equivalent system, or as
a single machine – infinite bus equivalent power system. Then the impedances from the position
of OOSPPAM (78) in the direction of the normal load flow (that is from the measurement point to
the remote system) can be taken as forward. The lens characteristic, as shown in Figure
200 and
Figure202, is obtained so that two equal in size but differently offset Mho characteristics are set
to overlap. The resultant lens characteristic is the loci of complex impedance Z(R, X) for which the
rotor (power) angle is constant, for example 110 degrees or 120 degrees; if the rotor (power) angle
approaches this value, then there is a high risk to have an out of step condition. The limit-of- reach
circle is constructed automatically by the algorithm; it is about 10% wider than the the circle that
has the line SE-RE as diameter (that is the out-of-step characteristic which corresponds to the
rotor (power) angle of 90 degrees). Figure
203 illustrates construction of the lens characteristic
for a power system.
1MRK 502 066-UUS B Section 7
Impedance protection
381
Technical manual
To Next Page
Loading...
