Siemens SIPROTEC 4 7UT6 Series, Руководство пользователя

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[diff-trafo-schaltgranpass-ynd5-020926-rei, 1, en_GB]
Figure 2-30 Matching the transformer vector group, example YNd5 (magnitudes not considered)
Figure 2-31 shows an example of an earth fault on the delta side outside the protected zone if an earthed
starpoint former (zigzag winding) is installed within the protected zone. Here, a zero sequence current occurs
on the right side but not on the left, as above. If the starpoint former were outside the protected zone (i.e. CTs
between power transformer and starpoint former), the zero sequence current would not pass through the
measuring point (CTs) and would not have any harmful effect.
[diff-trafo-erdkurzschuss-beisp2-020926-rei, 1, en_GB]
Figure 2-31 Example of an earth fault outside the protected transformer with a neutral earthing reactor
within the protected zone
The disadvantage of elimination of the zero sequence current is that the protection becomes less sensitive
(factor
2 /
3
because the zero sequence current amounts to 1 /
3
in case of an earth fault in the protected area.
Therefore, elimination is suppressed in case the starpoint is not earthed (see Figure 2-28 ), or the starpoint
current can be included ( Figure 2-29 ). If, for example, a surge voltage arrester is connected to the starpoint,
one should do without the advantage of that option in order to avoid recognition of a breakdown of the surge
voltage arrester as an internal fault. For this purpose, the starpoint of the respective side must be set to
Earthed
(addresses 313
STARPNT SIDE 1
, 323
STARPNT SIDE 2
, 333
STARPNT SIDE 3
, 343
STARPNT
SIDE 4
, 353
STARPNT SIDE 5
).
Functions
2.2 Differential Protection
SIPROTEC 4, 7UT6x, Manual 105
C53000-G1176-C230-5, Edition 09.2016