ABB Relion, Техническое руководство

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Real part (R) of Z in Ohms →
Im
ag
ina
ry
pa
rt
(X
) o
f Z
in
O
hm
s
→
^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
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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 (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 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-UUS A
Impedance protection
180
Technical manual