(Equation 281)
The calculated positive-sequence impedance amplitude Z1_AMPL and angle
Z1_ANGLE are available in primary ohms and degrees, respectively, in the Monitored
data view.
The calculated impedance is converted to ohms as the operating
characteristics are defined with the ohm settings.
Power swing detection
Power swing detection function comprises an inner and outer quadrilateral /circular
measurement characteristic. The positive sequence impedance is continuously
monitored for detecting a power swing condition. During normal power system
operation, the impedance is outside of outer characteristic. When the impedance
enters outer characteristic, output SWING_ST is activated, and the power swing
detection timer is triggered. The SWING_ST output will be deactivated if the
impedance leaves the zone between inner and outer characteristic. If the impedance
remains between the inner and outer characteristics longer than the time defined
by the setting
Swing time
, and the impedance enters inner characteristic, output
PSB is activated. The PSB output will be deactivated after the impedance leaves
outer characteristic for the time defined by
Pulse time
setting.
When an unbalanced fault occurs during power swing, the PSB output should
be deactivated to allow tripping. For the purpose module is monitoring negative
sequence current which is calculated from fundamental frequency three phase
currents. Negative sequence current level can be monitored if
Ng Seq current Spvn
is set to "Enable". When the negative sequence current is above the
Max Ng Seq
current
setting longer than the time delay defined by the setting
Neg Seq current
time
, the Power swing detection module is disabled. The module is disabled until
negative sequence current drops below the setting value. The
Max Ng Seq current
setting should be set above the maximum negative sequence current which may
appear during power swing.
Slow power swing can be used as criterion for disabling power swing detection.
Monitoring is activated by setting
Slow swing Spvn
to "Enable". If the positive
sequence impedance enters and remains inside outer characteristic longer than
the time delay defined by the setting
Slow swing time
, the Power swing detection
module is disabled. The module is disabled until the positive sequence impedance
moves outside outer characteristics. The setting
Slow swing time
should be
coordinated with network or cable current rating characteristics. Too long lasting
large current may need to be cleared even if situation is classified as power swing.
In case of heavily loaded lines, the optional load encroachment logic can be enabled
with the
Load discrimination
setting. The logic reserves an area for load impedance
defined by the
Outer Fw Ld Ris Rch, Outer Rv Ld Ris Rch, Inner Fw Ld Ris Rch, Inner
Rv Ld Ris Rch, Load angle1
and
Load angle2
settings.
Quadrilateral characteristic
If the
Pe Swg impedance Chr
is ‘Quadrilateral’, DSTRPSB has a double-polygon
characteristic.
Protection functions
1MRS759142 F
1048 REX640
Technical Manual
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