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3-10
Protection Functions
Directional Overcurrent
Protection I
> (67)
dir
857-UM001A-EN-P – July 2009
The Directional overcurrent protection can be used for
directional short circuit protection. Typical applications are:
Short circuit protection of two parallel cables or overhead lines
in a radial network.
Short circuit protection of a looped network with single feeding
point.
Short circuit protection of a two-way feeder, which usually
supplies loads but is used in special cases as an incoming feeder.
Directional earth fault protection in low impedance earthed
networks. Please note that in this case the device has to
connected to line-to-neutral voltages instead of line-to-line
voltages. In other words the voltage measurement mode has to
be "3LN" (See "Voltage Measurement Mode" in Chapter 5).
The stages are sensitive to the amplitude of the highest fundamental
frequency current of the three measured phase currents. The phase
angle is based on the phase angle of the three-phase power phasor.
For details of power direction see "Direction of Power and Current"
in Chapter 5. A typical characteristic is shown in Figure 3.7. The
base angle setting is –30°. The stage will pick up, if the tip of the
three phase current phasor gets into the grey area.
NOTE: If the maximum possible earth fault current is greater than
the used most sensitive directional over current setting, the device
has to be connected to the line-to-neutral voltages instead of line-to-
line voltages in order to get the right direction for earth faults, too.
(For networks having the maximum possible earth fault current less
than the over current setting, use 67N, the directional earth fault
stages.)
Im
+90°
-ind.
+cap.
-res.
-cap.
+ind.
-90°
Figure 3.7 – Example of protection area of the directional overcurrent function
2°
SET
VALUE
+res.
0°
Re
I
LOAD
TRIP AREA
-30
BASE ANGLE =
°
I
FAULT
ldir_angle2
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