3 Mounting and Commissioning
502
7SD5 Manual
C53000-G1176-C169-1
Figure 3-30 Polarity check for I
4
, example with current transformer configured in a
Holmgreen connection
Note
If parameters were changed for this test, they must be returned to their original state
after completion of the test !
I
4
from Parallel Line If I
4
is the current measured on a parallel line, the above procedure is done with the
set of current transformers on the parallel line (Figure 3-31). The same method as
above is used here, except that a single phase current from the parallel feeder is mea-
sured. 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 3-31 this is L1-E) should be
reduced by the influence of the parallel line. The impedances can be read out as
primary or secondary quantities in the list of operational measured values.
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.
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