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Functions
Power Swing
Blocking
Power Swing
Tripping
6-76
G
Trajectory stability
When the impedance trajectory enters the PPOL during a swing condition the
system must be in the area of steady state instability. In Figure 6-42 this
corresponds to the lower half of the circle.
All these conditions must be true for the generation of a power swing block condition.
Once the power swing block condition is set it will remain picked up until the
impedance vector leaves the power swing polygon (PPOL) unless a fault occurs
during this time. The detection of a jump in the trajectory or non-symmetry of the
trajectories will reset the power swing blocking condition.
For the out of step tripping (OST) signal, a power swing detection is required in the
normal manner. Subsequently the sign of the R component in the impedance is
evaluated at the instant that the trajectory entered and exited the PPOL. If this sign is
not the same, an out of step condition is detected and the power swing trip signal is
issued if this was configured.
The power swing blocking affects the distance protection. If the criteria for power
swing detection have been fulfilled in at least one phase, the following reactions are
possible in relation to the power swing blocking function (set in address 2002 P/S
Op. mode:
• Blocking of all zones ( All zones block ):
All zones of the distance protection are blocked during a power swing.
• Blocking of the first zone only ( Z1/Z1B block ):
The first zone (Z1) and the overreaching zone (Z1B) are blocked during a power
swing. Faults in other zones are tripped with the associated grading time.
• Blocking of only the higher zones ( Z2 to Z5 block ):
The higher zones (Z2 to Z5) are blocked during a power swing. Only the first and
the overreaching zone (Z1 and Z1B) remain active.
• Blocking of the first two zones ( Z1,Z1B,Z2 block ):
The first and second zone (Z1 and Z2) and the overreaching zone (Z1B) are
blocked during a power swing. The higher zones Z3 to Z5 remain active.
The associated measures taken apply to all phases when power swing has been de-
tected. They are active for as long as the measured impedance vector is inside the
power swing range PPOL, or if due to an abrupt change of the associated impedance
vector the power swing criteria are no longer satisfied.
If tripping in the event of an unstable power swing (out-of-step condition) is desired,
the parameter PowerSwing trip = Yes is set. If the criteria for power swing detec-
tion are satisfied, the distance protection is initially blocked according to the configured
program for power swing blocking, to avoid tripping by the distance protection.
When the impedance vectors identified by the power swing detection exit the power
swing characteristic PPOL, the sign of the R components in the vectors are checked
to see if they are the same on exiting and entering the characteristic. If this is the case,
the power swing process is inclined to stabilize. Otherwise, the vector passed through
the power swing characteristic (loss of synchronism, case (4) in Figure 6-40). The de-
vice issues a three-pole trip command, thereby isolating the two system segments
from each other. Power swing tripping is alarmed.
As the operating range of the power swing supplement depends on the distance pro-
tection settings, the power swing tripping can also only be active, when the distance
protection has been activated.
7SA6 Manual
C53000-G1176-C156-2
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