ABB REG650 Technical Manual page 139

1MRK 502 034-UEN -
Technical Manual
centre of oscillation is where the locus of the complex impedance Z(R, X) crosses
the (impedance) line connecting the points SE (Sending End), and RE (Receiving
End). The point on the SE – RE line where the trajectory of Z(R, X) crosses the
impedance line can change with time and is mainly a function of the internal
induced voltages at both ends of the equivalent two-machine system, that is, at
points SE and RE.
Measurement of the magnitude, direction and rate-of-change of load impedance
relative to a generator's terminals provides a convenient and generally reliable
means of detecting whether machines are out-of-phase and pole-slipping is taking
place. Measurement of the rotor (power) angle is important as well.
Rotor (power) angle δ can be thought of as the angle between the two lines,
connecting point 0 in Figure
SE and RE, respectively. These two lines are not shown in
values of the power angle, that is, under stable, steady-state, load conditions are
from 30 to 60 electrical degrees. It can be observed in
reaches 180 degrees when the complex impedance Z(R, X) crosses the impedance
line SE – RE. It then changes the sign, and continues from -180 degrees to 0
degrees, and so on. Figure 70
Z(R, X) against the time for the case from
4
3
normal
load
Z(R, X) under fault lies
2
on the impedance line
or near (for 3-ph faults)
1
0
fault 500 ms
fault
-1
occurrs
Under 3-phase fault
condition rotor angle
-2
of app. ±180 degrees
is measured ...
-3
-4
0 200 400
IEC10000110 V1 EN
Figure 70: Rotor (power) angle and magnitude of the complex impedance
Z(R, X) against the time
In order to be able to fully understand the principles of OOSPPAM, a stable case,
that is, a case where the disturbance does not make a generator to go out-of-step,
must be shown.
69, that is, Z(R, X) under normal load, with the points
shows the rotor (power) angle and the magnitude of
Figure
|Z| in Ohms
rotor (power)
angle in rad
angle
|Z|
Z(R,X) crossed
the impedance line, Z-line,
connecting points SE - RE
600 800 1000
Time in milliseconds →
Section 6
Impedance protection
Figure 69. Normal
Figure 70 that the angle
69.
1200 1400
IEC10000110-1-en.vsd
133