The method of measurement processes the sampled voltage values and filters out the fundamental compo-
nent numerically.
Measured Value 3I0, Method of Measurement
The function usually evaluates the ground current 3I0 sensitively measured via a core balance current trans-
former. Since the linearity range of the sensitive measuring input ends at approx. 1.6 A, for larger secondary
ground currents, the function switches to the 3I0 calculated from the phase currents. This results in a very
large linearity and settings range.
The method of measurement processes the sampled current values and filters out the fundamental compo-
nent numerically. The methods of measurement are characterized by high accuracy and by insensitivity to
harmonics, especially the 3rd and 5th harmonics frequently present in the ground-fault (residual) current.
Depending on the connection type of the measuring point as well as the current terminal blocks used,
different linearity and setting ranges result. You can find more information in section Measured Value 3I0,
Method of Measurement , Page 569.
Y0, G0, B0
The fundamental-component values of V0 and 3I0 are used to calculate the admittance Y0 = G0 + jB0. You can
choose to use G0 or B0 to determine the direction.
Ground-Fault Detection, Pickup
If the absolute value of the ground current 3I0 exceeds the threshold value 3I0> release thresh.
value and the absolute value of the zero-sequence voltage V0 exceeds the threshold value V0> threshold
value, the stage recognizes the ground fault. The calculation of G0 or B0 is started with exceeding the
threshold values and then, the direction determination (see the following) is performed. The direction result is
indicated via the
Ground fault
signal (in the General function block). If the direction result equals the para-
meterized direction (parameter Directional mode), the stage picks up.
Direction Determination
Exceeding the threshold values by the zero-sequence voltage V0 is a criterion for the ground fault. The direc-
tion determination can be delayed from the occurrence of the zero-sequence voltage with the Dir. deter-
mination delay parameter to achieve steady-state measurands. The result from the direction determina-
tion is only valid if the absolute value of the ground current 3I0 has also exceeded its release threshold value.
The following figure shows an example of the direction determination in the complex phasor diagram for the
G0 direction measurement method with a correction value of the direction straight line from 0 (Parameter φ
correction). The example is suitable for the determination of the ground-fault direction in an arc-suppres-
sion-coil-ground system where the value G0 is decisive for the direction determination.
[DwY0Dire-171012-01, 1, en_US]
Figure 6-137 Direction-Characteristic Curve for the G0 Measurement
Protection and Automation Functions
6.15 Sensitive Ground-Fault Detection
SIPROTEC 5, Overcurrent Protection, Manual 593
C53000-G5040-C017-8, Edition 07.2017
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