ABB REG650 Technical Manual page 165

1MRK 502 043-UUS B
Technical Manual
The second method
This method is more exact. If the break-time of the circuit breaker is known, (and
specified as the setting tBreaker) than it is possible to initiate a trip (break) command
almost exactly tBreaker milliseconds before the rotor (power) angle reaches 0 degrees,
where the currents are at their minimum possible values. The breaker contacts will
open at almost exactly 0 degrees, as illustrated in
point in time when the breaker opening process must be initiated is estimated by
solving on-line the so called "synchronizer" differential equation. Note that if tBreaker
is left on the initial (default) value, which is zero (0), then the alternative setting
TripAngle will decide when the trip command will be given. If specified tBreaker > 0,
for example tBreaker = 0.040 second, then automatically, the TripAngle will be
ignored and the second, more exact method applied.
0.6
trip
region
0.4
3
here rotor
0.2
angle
is -90°
0 no trip
region
inside
circle
-0.2
outside the
circle is the trip
-0.4
region for
TripAngle <= 90°
-0.6 -0.4 -0.2
IEC10000114 V1 EN
Figure 73: The imaginary offset Mho circle represents loci of the impedance Z(R,
X) for which the rotor angle is 90 degrees
X[Ohm]
RE - Receiving End (infinite bus)
loci of Z(R, X)
no trip
region
2
no trip
rotor angle
region
= ±180°
relay
← Z - line connects
points SE & RE
SE - Sending End (generator)
0 0.2 0.4
Real part (R) of Z in Ohms →
Impedance protection
Figure 74 for tBreaker = 0.060 s. The
1
here
rotor angle
is +90°
R[Ohm]
this circle
←
is loci of
the rotor
angle = 90°
0.6 0.8
IEC10000114-1-en.vsd
Section 7
159