Siemens siprotec 7SA6 User Manual page 599

I Measured on a
4
Parallel Line
7SA6 Manual
C53000-G1176-C133-1
Busbar
Line
Figure 8-25 Polarity testing for I
Holmgreen-connection
Attention! If parameters were changed for this test, they must be returned to their
original state after completion of the test!
If I is the current measured on a parallel line, the above procedure is done with the
4
set of current transformers on the parallel line (Figure 8-26). The same method as
above is used here, except that a single phase current from the parallel feeder is
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 8-26 this is L1–E) should be
reduced by the influence of the parallel line. The impedances can be observed as
primary 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
polarity. After isolation of both lines and short-circuiting of the current transformer
secondary circuits, the connections must be checked and rectified. Subsequently the
measurement must be repeated.
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I
L1
I
L2
I
L3
I
4
7SA6
, example with current transformers configured in a
4
Installation and Commissioning
L1
L2
L3
U U U U
L1 L2 L3 N
I '
L1
I '
L2
I '
L3
I '
4
has a swapped
4
8-55