Siemens SIPROTEC 7SK80 - Page 87

Functions
2.3 Directional Gound Overcurrent Protection 67N
SIPROTEC, 7SK80, Manual
E50417-G1140-C344-A4, Release date 08.2010
87
Table 2-5 Measured values for determining the fault direction
1)
or 3 · V
0
= |VA + VB + VC|, depending on type of connection for the voltages
Direction Determination via Ground Element using Ground Values
Figure 2-21 shows the treatment of the reference voltage for the directional ground element, also based on a
single-phase ground fault in phase A. The fault voltage serves as reference voltage. Depending on the connec-
tion of the voltage transformer, this is the voltage 3V
0
(as shown in Figure 2-21) or V
N
. The fault current -3I
0
is
phase offset by 180° to the fault current I
scA
and follows the fault voltage 3V
0
by fault angle ϕ
sc
. The reference
voltage is rotated by the setting value 1619 ROTATION ANGLE. In this case, a rotation by -45°.
Figure 2-21 Rotation of the reference voltage, directional ground element with zero sequence values
The forward area is equally a range of ±86° around the rotated reference voltage V
ref,rot
If the vector of the fault
current -3I
0
(or I
N
) is in this area, the device detects forward direction.
Pickup N
Current Voltage
N I
N
V
N
1)
A, N I
N
V
N
1)
B, N I
N
V
N
1)
C, N I
N
V
N
1)
A. B, N I
N
V
N
1)
B, C, N I
N
V
N
1)
A, C, N I
N
V
N
1)
A, B, C, N I
N
V
N
1)