ABB REG650 ANSI, Technical Manual

Page: 172 / 728

-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 →
Im
ag
ina
ry
pa
rt
(X
) o
f Z
in
O
hm
s
→
^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
- -
-
-
-
-
-
-
-
-
-
-
-
-
-
- - -
-
-
-
-
-
-
-
-
-
-
-
-
-
-
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
→
IEC10000111-1-en.vsd
IEC10000111 V1 EN
Figure 78: 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 78 , 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.
7.4.7.1 Lens characteristic
A precondition in order to be able to construct a suitable lens characteristic is that the
power system in which OOSPPAM 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 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 76 and Figure 78 , 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; these are the
angles where stability problems are very likely.
Figure 79 illustrates construction of
the lens characteristic for a power system.
Section 7
1MRK 502 048-UEN A
Impedance protection
166
Technical manual