Siemens siprotec 7SA522 - Page 112

2 Functions
112
7SA522 Manual
C53000-G1176-C155-3
In Figure 2-40 a simplified logic diagram for the power swing function is given. This
measurement is done on a per phase basis although 2-40 only shows the logic for one
phase. Before a power swing detected signal is generated, the measured impedance
must be inside the power swing polygon (PPOL).
In the following 4 measuring criteria are listed:
Trajectory continuity The calculated R and X values must create a constant
line. There must be no jump from one measured value
to the next. Refer to Figure 2-38.
Trajectory monotony The impedance trajectory must initially not change R-
direction. Refer to Figure 2-38.
Trajectory symmetry The trajectory of each phase is evaluated. If no fault is
present these 3 trajectories must be symmetrical.
During single pole open conditions the remaining 2 tra-
jectories must be symmetrical.
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 2-39 this cor-
responds 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 imped-
ance vector leaves the power swing polygon (PPOL). This is unless a fault occurs
during this phase. The detection of a jump in the trajectory or non-symmetry of the
trajectories will reset the power swing blocking condition. The power swing detection
can be blocked via a binary input.
Power Swing
Blocking
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  36
2SPRGH):
• Block all zones ($OO]RQHVEORFN): All zones of the distance protection are
blocked during a power swing.
• Blocking of the first zone only (==%EORFN): The first zone (Z1) and the over-
reaching zone (Z1B) are blocked during a power swing. Faults in other zones are
tripped with the associated grading time.
• Blocking of the higher zone only (=WR=EORFN): The higher zones (Z2 to Z5)
are blocked during a power swing. Only the first and the overreaching zone (Z1 and
Z1B) remain active.
• Blocking of the first two zones only (==%=EORFN): The first and second
zone (Z1 and Z2) and the overreaching zone (Z1B) are blocked during a power
swing. The higher zones Z3 to Z5 remain active.
Only the phases in the configured zones are blocked in which power swings were de-
tected. The associated measures taken apply to all phases when power swing has
been detected. They are active for as long as the measured impedance vector is
inside the power swing range PPOL, or if due to an abrupt change of the associated
impedance vector the power swing criteria are no longer satisfied. But the influence of
the power swing block on the distance protection relay will be prolonged for a defined
time (address  7ULS'(/$<36). Thus transient states (e.g. switching opera-
tions) are compensated, which occur during a power swing and cause a jump in the
measured quantities.