Siemens 7SC80 Manual page 124

Functions
2.3 Directional Overcurrent Protection 67, 67N
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).
[7sj6x_vorwaertscharakteristik-gumz-phase-220904-he, 1, en_US]
Figure 2-32
Direction Determination of Directional Ground Element with Ground Values
Figure 2-33 shows the treatment of the reference voltage for the directional ground element, also based on a
single-phase ground fault in phase A. Contrary to the directional phase elements, which work with the
unfaulted voltage as reference voltage, the fault voltage itself is the reference voltage for the directional
ground element. Depending on the connection of the voltage transformer, this is the voltage 3V
Figure 2-33) or V
voltage 3V by fault angle ϕ
0
In this case, a rotation by -45°.
[7sj6x_drehung-referenzspannung-erde-nullsys-220904-he, 1, en_US]
Figure 2-33
The forward area is also a range of ±86° around the rotated reference voltage V
current -Ι (or Ι
0 N
124
Forward characteristic of the directional function, directional phase element
. The fault current -3Ι is phase offset by 180° to the fault current Ι
N 0
. The reference voltage is rotated by the setting value 1619 ROTATION ANGLE.
sc
Rotation of the reference voltage, directional ground element with zero sequence values
) is in this area, the device detects forward direction.
(as shown in
0
and follows the fault
scA
. If the vector of the fault
ref, rot
SIPROTEC Compact, 7SC80, Manual
E50417-G1140-C486-A8, Edition 07.2017
ref,rot