ABB Relion 670 Series RES670, Technical Manual

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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-step and pole-slipping is taking place. Measurement of the
rotor (power) angle δ is important as well.
Rotor (power) angle δ can be thought of as the angle between the two lines, connecting
point 0 in Figure
41 , that is, Z(R, X) under normal load, with the points SE and RE,
respectively. These two lines are not shown in Figure 41 . Normal 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 Figure
42 that the angle 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
42 shows the rotor
(power) angle and the magnitude of Z(R, X) against time for the case from Figure 41 .
0 200 400 600 800 1000 1200 1400
-4
-3
-2
-1
0
1
2
3
4
Time in millis econds
®
Im
pe
da
nc
e
Z
in
O
hm
a
nd
r
ot
or
a
ng
le
in
r
ad
ia
n
®
|Z| in Ohms
angle in rad
normal
load
fault 500 ms
Z(R,X) cros s e d
the im pe da nce line , Z-line ,
conne cting points S E - RE
fault
occurrs
Z(R, X) under fault lies
on the impedance line
or near (for 3-ph faults )
Unde r 3-pha s e fa ult
condition rotor a ngle
of a pp. ±180 de gre e s
is m e a s ure d ...
rotor (power)
angle
|Z|
IEC10000110-2-en.vsd
1
2
3
1
0
IEC10000110 V2 EN
Figure 42: 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 (78), a stable case, that
is, a case where the disturbance does not make a generator to go out-of-step, must be
shown.
Section 7
1MRK 511 365-UUS A
Impedance protection
160 Phasor measurement unit RES670 2.1 ANSI
Technical manual