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Figure 3-34
Polarity check of I
I
from a Power Transformer Starpoint
4
If I
is the earth current measured in the star-point of a power transformer and intended for the earth fault pro-
4
tection direction determination (for earthed networks), then the polarity check can only be carried out with zero
sequence current flowing through the transformer. A test voltage source is required for this purpose (single-
phase low voltage source).
Caution!
Feeding of zero sequence currents via a transformer without broken delta winding.
Inadmissible heating of the transformer is possible!
Zero sequence current should only be routed via a transformer if it has a delta winding, therefore e.g. Yd, Dy
or Yy with a compensating winding.
DANGER!
Energized equipment of the power system! Capacitive coupled voltages at disconnected equipment of the
power system !
Non-observance of the following measure will result in death, severe personal injury or substantial property
damage.
Primary measurements must only be carried out on disconnected and earthed equipment of the power system!
The configuration shown in Figure 3-35 corresponds to an earth current flowing through the line, in other words
an earth fault in the forward direction.
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
, example with earth current of a parallel line
4
Mounting and Commissioning
3.3 Commissioning
555
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