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Installation and Commissioning
Bus-
bar
Parallel line
Figure 8-26
Polarity check of I
I
Measured in a
4
Power Transformer
Star-Point
8-56
I
L1
I
L2
I
L3
I
'
L1
I
'
L2
I
'
L3
6$
, example with earth current of a parallel line
4
If I
is the earth current measured in the star-point of a power transformer and intended
4
for the earth fault protection direction determination (for earthed systems), then the
polarity check can only be carried out with a zero sequence current flowing through
the transformer. A test voltage source is required for this purpose (single-phase low
voltage source).
Caution!
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. Otherwise inadmissible
heating of the transformer may result.
DANGER!
Primary measurements must only be carried out on disconnected and grounded
equipment of the power system. Danger to life exists even on disconnected
equipment because of capacitive coupling from other energized equipment of
the power system!
The configuration shown in Figure 8-27 corresponds to an earth current flowing
through the line, in other words an earth fault in the forward direction.
At least one stage of the earth fault protection must be set to be directional (address
[ of the earth fault protection). The test current on the line must exceed the pick-
up threshold setting of this/these stages; if required, the pick-up threshold setting must
be reduced. The parameters that are changed, must be noted.
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ƒuh†r
U
e
I
L1
I
L2
I
L3
I
'
L1
I
'
L2
I
'
L3
9r‰vprÈqr…Çr†‡
I
4
I
'
4
Line
L1
L2
L3
n
U
U
U
U
U
n
L1
L2
L3
n
6$
7SA6 Manual
C53000-G1176-C133-1
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