Siemens siprotec 7SA6, Руководство пользователя

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Installation and Commissioning
8-66
7SA6 Manual
C53000-G1176-C156-2
measured. The parallel line must carry load while the protected line should carry load.
The line remains switched on for the duration of the measurement.
If the polarity of the parallel line earth current measurement is correct, the impedance
measured in the tested loop (in the example of Figure 8-33 this is L1–E) should be re-
duced by the influence of the parallel line. The impedances can be observed as pri-
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 8-33 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 (for earthed systems), then the po-
larity 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 volt-
age source).
I
L2
'
Bus-
bar
Line
L1
L2
L3
e
n
7SA6
(Device under test)
I
L1
I
L3
U
e
I
L2
U
n
I
4
U
L1
U
L2
U
L3
U
n
(alternatively
disconnect
here)
Parallel line
I
L1
I
L3
I
L2
I
L1
'
I
L3
'
I
L2
'
I
L3
'
I
4
'
I
L1
'
7SA6
bypass one
phase
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.