Technical description
2 Protection functions
2.4 Distance protection Z<
VM259.EN007
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Characteristic type 4.
In the characteristic type 4 the line angle is set to 75 degrees.
The reactive setting X is set significantly above the resistive
setting R. The resistive reach is equal at the both sides of the
line setting until the resistive reach of quadrant II hits the line
X. The load setting R and the angle setting of load block can be
found from ―distance common settings‖ menu. These values are
being used only if the ―Load block in use‖ is selected as ―Yes‖.
The tolerance of inaccuracy is now taken from the X setting.
This is because the X value is greater than the R value. If the
allowed inaccuracy is for example 5 % and X setting is 40 Ω the
allowed tolerance would be 2.0 Ω. Notice that with these
settings the load block area is fully covered with the tolerance
so all settings are not reasonable.
The behavior of power swing blocking and out of
step tripping functions
Power swing is using the setting value ―Power swing setting
dZ‖. Power swing function is enabled when the ―Enable for
power swing‖ is active. Depending of the setting ―dZ‖ there is a
certain sized area outside the biggest used distance zone. If the
dZ is set to 1.0 Ω the ―swing area‖ starts one ohm away from
the edge of the biggest zone. The idea of this area is to notice
the power swing before it reaches the zone to have enough time
to activate the internal blocking. Power swing blocking is used
to block desired distance zones by connecting the ―power swing‖
line to the distance zones at the block matrix (see Figure
2.4.4-1).
Power swing blocking is active when the speed of the swing is
less than the set value for example 1.0 Ω / 40 ms (40 ms is fixed
value). If the speed of the swing exceeds the 1.0 Ω / 40 ms limit
there won‘t be block and the distance stage trips normally.