Siemens SIPROTEC 7SC80 Series Manual page 80

Functions
2.3 Directional Overcurrent Protection 67, 67N
Figure 2-17 Rotation of the reference voltage, directional phase element
The rotated reference voltage defines the forward and reverse area, see Figure 2-18. The forward area is a
range of ±86° around the rotated reference voltage V
device detects forward direction. In the mirrored area, the device detects reverse direction. In the intermediate
area, the direction result is undefined.
In a network, the vector of the fault current is usually in the forward or reverse area. If the vector moves out of
one these areas, e.g. the forward area, in direction of the undefined area, it leaves the forward area at V
±86° and reaches the undefined area. If the vector leaves the undefined area in direction of the forward area
(or reverse area), a hysteresis of 2° is added. This hysteresis prevents chattering of the directional result. The
current vector reaches the forward area at ±84° (= 86°-2° hysteresis).
Figure 2-18 Forward characteristic of the directional function, directional phase element
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If the vector of the fault current is in this area, the
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E50417-G1140-C486-A1, Release date 12.2011
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SIPROTEC, 7SC80, Manual