Allen-Bradley Rockwell Automation 857 User Manual page 61

Two modes are available: directional and non-directional (Figure 3.8).
In the non-directional mode the stage is acting just like an ordinary
overcurrent 50/51 stage.
+90°
-ind.
+cap.
2°
DIRECTIONAL
SET
VALUE
-res.
BASE ANGLE = ° 0
TRIP AREA
-cap.
+ind.
-90°
Figure 3.8 – Difference between directional mode and non-directional mode
An example of bi-directional operation characteristic is shown in
Figure 3.9. The right side stage in this example is the stage Idir> and
the left side is Idir>>. The base angle setting of the Idir> is 0° and
the base angle of Idir>> is set to –180°.
+90°
-ind.
4°
I >> TRIP AREA
DIR
SET
VALUE
-res.
- 0
BASE ANGLE = 18 °
-cap.
-90°
Figure 3.9 – Bi-directional application with two stages Idir> and Idir>>
When any of the three phase currents exceeds the setting value and –
in directional mode – the phase angle including the base angle is
within the active ±88° wide sector, the stage picks up and issues a
start signal. If this fault situation remains on longer than the delay
setting, a trip signal is issued.
0°
+res.
-res.
+cap.
SET
0°
VALUE
+res.
BASE ANGLE = ° 0
I > TRIP AREA
DIR
+ind.
ldir_modeBiDir
15%
3-11
Protection Functions
+90°
-ind.
+cap.
NON-DIRECTIONAL
SET
0°
VALUE
+res.
TRIP AREA
-cap.
+ind.
-90°
ldir_modeA
15%
857-UM001A-EN-P – July 2009