[logfp3i0f-280314-01, 4, en_US]
Figure 6-126
Logic Diagram of the Directional 3I0 Stage with Cos φ or Sin φ Measurement
Measured Value V0, Method of Measurement
The device can measure the residual voltage at the broken-delta winding. The measured voltage VN is
converted to a value with reference to the zero-sequence voltage V0. If the residual voltage is not available to
the device as a measurand, the zero-sequence voltage V0 is calculated from the measured phase-to-ground
voltages V
A
, V
B
, and V
C
using the defining equation.
This 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 sensitively measured ground current 3I0 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 current calculated from the phase currents. This results in a
very large linearity and settings range.
Protection and Automation Functions
6.15 Sensitive Ground-Fault Detection
SIPROTEC 5, Overcurrent Protection, Manual 569
C53000-G5040-C017-8, Edition 07.2017
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