Siemens siprotec 7SA522, User Manual

Page: 487 / 628

Installation and Commissioning
8-31
7SA522 Manual
C53000-G1176-C119-2
mary or secondary quantities in the list of operational measured values (Section
7.1.3.1).
If, on the other hand, the measured impedance increases when compared to the value
without parallel line compensation, the current measuring input I
4
has a swapped po-
larity. After isolation of both lines and short-circuiting of the current transformer sec-
ondary circuits, the connections must be checked and rectified. Subsequently the
measurement must be repeated.
Figure 8-16 Polarity check of I
4
, example with earth current of a parallel line
I
4
Measured in a
Power Transformer
Star-Point
If I
4
is the earth current measured in the star-point of a power transformer and intended
for the earth fault protection direction determination, 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).
I
L2
’
Bus-
bar
Line
L1
L2
L3
e
n
6$
'HYLFHXQGHUWHVW
I
L1
I
L3
U
e
I
L2
U
n
I
4
U
L1
U
L2
U
L3
U
n
DOWHUQDWLYHO\
GLVFRQQHFW
KHUH
Parallel line
I
L1
I
L3
I
L2
I
L1
’
I
L3
’
I
L2
’
I
L3
’
I
4
’
I
L1
’
6$
E\SDVVRQH
SKDVH
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!