Mounting and Commissioning
3.3 Commissioning
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
554
Figure 3-33 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
of the parallel line (Figure 3-34). 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 3-34 this is L1-E) should be reduced by the influence of the parallel line (power
flow in both lines in the same direction). The impedance can be read out as primary or secondary quantity 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 polarity. After isolation of both lines and short-
circuiting of the current transformer secondary circuits, the connections must be checked and rectified. Subse-
quently the measurement must be repeated.
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