2.4 Distance protection Z<
2 Protection functions
Technical description
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Note! Out of step activates at the edge of the power swing area, NOT at the
edge of the distance zone. Out of step function can be connected to a
tripping signal at the output matrix.
1.
Power swing may reach the zone from any direction but
only as long as it leaves the zone at the first quadrant it will
remain as a power swing. In case that the swing stops in
the middle of zone and none of the terms of fault are active
the block will remain until the zone is left or fault occurs.
2.
Situation starts as a power swing but the swing comes out
from the second quadrant. Therefore out of step is activated.
When out of step is activated the activation lasts for 0.5
seconds.
3.
Fault during the power swing.
4.
Basically power swing function is always undirectional.
This means quadrants I and III are working similar way
regardless the direction mode of distance stage (passing
quadrant III with certain speed always activates power
swing block). This makes the power swing to function when
using reverse or undirectional mode.
Note! The conditions for the power swing blocking to be activated require in
addition of the previously mentioned rate of change of impedance
(dZ/dt) condition that sequences unbalance (I2/I1) is less than 25% and
calculated residual current (IoCalc) is less than 10%. These mentioned
parameters I2/I1 and IoCalc are fixed in the relay and can not be set by
users.
Figure 2.4.4-1 How to use power swing blocking with certain zones.