Functions
2.14 Differential Protection and Its Protected Objects
SIPROTEC, 7UM62, Manual
C53000-G1176-C149-7, Release date 03.2010
121
Figure 2-44 Vector group matching for Y(N) d5 (with earthed starpoint)
In the following figure on the left-hand side, a zero sequence current will occur in case of e.g. an external fault;
on the right-hand side, it will not. If the currents were compared without first eliminating the zero sequence cur-
rent, the result would be wrong (differential current despite external fault). Therefore, the zero sequence current
must be eliminated on side 1. The zero sequence current is subtracted from the phase currents. The rule for
calculation is shown in the left-hand matrix in Figure 2-44.
Figure 2-45 Example of an earth fault outside the transformer with distribution of currents
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