Lens Characteristic - ABB REG650 Technical Manual

Section 6
Impedance protection
6.3.6.1
134
1
SE
G
0.8
fault
relay
0.6
-
zone 2
-
0.4
-
-
-
-
X-line →
0.2 ^ ^ ^ ^ ^ ^ ^ ^ ^
-
-
- -
0
-
-
limit of
-
-
-0.2 reach
-
zone 1
-
-
- -
-0.4
-0.6
this circle forms
-0.8
the right-hand side
edge of the lens
-1
-1 -0.5
IEC10000111 V1 EN
Figure 71: A stable case where the disturbance does not make the generator
to go out-of-step
It shall be observed that in a stable case, as shown in
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.

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
obtained so that two equal in size but differently offset Mho characteristics are set
to overlap. The resultant lens characteristic is the loci of constant rotor (power)
angle. An advantage of this characteristic is that the lens 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 72 illustrates construction of the lens characteristic for a power system.
RE
X [Ohm]
RE
-
- -
- -
- -
- - -
- - - -
- - - -
- -
- - -
-
- - -
- - - 4
-
- - -
- - -
-
- - -
- - - -
- -
2
- - - -
- - 1
- - -
-
- - -
fault →
- -
-
- -
3
- -
- -
-
^ ^ ^ ^ ^ ^ ^ ^ ^
- -
- -
-
- -
- -
Z-line →
- -
- -
- -
- -
- -
-
- -
- -
- -
- - -
- -
- -
-
relay lens → - -
- -
- -
-
- -
110° - - -
- -
-
- - -
- - -
-
- - - - - -
-
- - -
- - -
- -
- - - -
- - -
- - - -
- - - -
- -
- -
- - -
SE
0 0.5
Real part (R) of Z in Ohms
1MRK 502 034-UEN -
Z(R,X) 20 ms
after line out
pre-fault
Z(R,X)
5
0
6
R
0 → pre-fault Z(R, X)
3 → Z(R, X) under fault
5 → Z 20 ms after line out
6 → pow er line reclosed
1 1.5
→
IEC10000111-1-en.vsd
Figure 71, where the
Figure 69 and Figure
Technical Manual
71, is