ABB REG670 Technical Manual page 276

Section 7
Impedance protection
270
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
IEC10000114 V1 EN
Figure 116: The imaginary offset Mho circle represents loci of the impedance
Z(R, X) for which the rotor angle is 90 degrees
35
pos. seq. current in kA
trip command to CB
30
rotor angle in radian
25
20
current increases under
fault conditions
15
fault
occurs
10
← normal load current
5
← rotor angle
0
-5
0 200
IEC10000115 V1 EN
Figure 117: Trip initiation when the break-time of the circuit breaker is known
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)
-0.2 0 0.2 0.4
Real part (R) of Z in Ohms →
← after 1st
fault cleared →
current decreases
trip command →
issued here
→
angle towards 0°
400 600 800
Time in milliseconds
→
1MRK502052-UEN B
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
very high currents due
to out-of-step condition
pole slip
← 2nd
← min. current
← tBreaker = 60 ms
1000 1200
IEC10000115-1-en.vsd
Technical manual