Functions
2.30 100-%-Stator Earth Fault Protection with 3rd Harmonics (ANSI 27/59TN 3rd Harm.)
SIPROTEC, 7UM62, Manual
C53000-G1176-C149-7, Release date 03.2010
220
Figure 2-95 3rd harmonic secondary voltage as a function of the active power (reactive power as parame-
ter)
As Figure 2-95 shows, the rise is almost equal in both cases. The most unfavourable case is operation in un-
derexcitation conditions.
In Figure 2-96 this curve is extrapolated to 100 % S
N device
Using the data of the reference system in chapter 2.1, we obtain S
N Gen
= 5.27 MVA and S
N device
= √3·U
VT prim
· I
CT prim
= √3 · 6.3kV · 500A = 5.46 MVA.
The x-axis in Figure 2-95 must be multiplied with factor S
N Gen
/S
N device
= 5.27 MVA/5.46 MVA = 0.965 for res-
caling.
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