Ground-Fault Detection, Pickup
If the absolute value of the ground current 3I0 vector exceeds the threshold value 3I0> threshold value
and the absolute value of the zero-sequence voltage V0 vector exceeds the threshold value Min. V0> for
dir. determ., the stage detects the ground fault . The direction determination (see in the following para-
graph) is started when the zero-sequence voltage exceeds the threshold. The result from the direction deter-
mination is only valid if the absolute value of the ground current 3I0 vector has also exceeded its threshold
value. The direction result is indicated via the
Ground fault
signal (in the General function block).
As long as the direction result equals the parameterization 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 direction is determined via the determination of the phase angle between the angle-error compensated
ground current 3I0com. and the rotated zero-sequence voltage V0, indicated in the following as reference
voltage V
ref,rot
. To take different system conditions and applications into account, the reference voltage can be
rotated through an adjustable angle (Rotation angle of ref. volt. parameter). This moves the vector
of the rotated reference voltage close to the vector ground current -3I0com. Consequently, the result of direc-
tion determination is as reliable as possible.
The rotated reference voltage V
ref,rot
and the Forward section +/- parameter define the forward and
reverse area. The forward area results as range ± Δφ around the rotated reference voltage V
ref,rot
. The value ±
Δφ is set with the Forward section +/- parameter. The remaining area besides the forward area is the
reverse area. Between the forward and reverse area, a hysteresis is defined, refer to Figure 6-135.
[dwdirrot-011112-02.vsd, 1, en_US]
Figure 6-135
Directional Characteristic in Forward Mode
Protection and Automation Functions
6.15 Sensitive Ground-Fault Detection
588 SIPROTEC 5, Overcurrent Protection, Manual
C53000-G5040-C017-8, Edition 07.2017
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