Design - ABB Relion Technical Manual

Section 7
Impedance protection
7.4.7.5
186
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 82: Trip initiation when the break-time of the circuit breaker is known

Design

When the complex impedance Z(R, X) enters the limit-of-reach region, the algorithm
determines the direction impedance Z moves, that is, the direction the lens is traversed and
measures the time taken to traverse the lens from one side to the other. If the traverse time
is more than the limit 40 or 50 ms, a pole-slip is declared. If the complex impedance Z(R,
X) exits the lens on the same side it entered, then it is a stable case and the protected
machine is still in synchronism. If a pole-slip has been detected, then it is determined in
which zone the centre of oscillation is located. If the number of actual pole-slips exceeds
the maximum number of allowed pole-slips in either of the zones, a trip command is
issued taking care of the circuit breaker safety.
very high currents due
to out-of-step condition
← after 1st
pole slip
fault cleared →
current decreases
trip command →
issued here
→
angle towards 0°
400 600 800
Time in milliseconds →
1MRK 502 048-UUS A
← 2nd
← min. current
← tBreaker = 60 ms
1000 1200
IEC10000115-1-en.vsd
Technical manual