2 Functions
212
7SD5 Manual
C53000-G1176-C169-1
Zero Sequence
Voltage Time Pro-
tection ( U
0
- i n v e r s e )
The zero sequence voltage time protection operates according to a voltage-depen-
dent trip time characteristic. It can be used instead of the time overcurrent stage with
inverse time delay.
The voltage/time characteristic can be displaced in voltage direction for a determined
constant voltage U0inv. minimum, valid for t→ ∞ and in time direction by a deter-
mined constant time T forw. (U0inv)). The characteristics are shown in the Tech-
nical Data.
Figure 2-91 shows the logic diagram. The tripping time depends on the level of the
zero sequence voltage U
0
. For meshed earthed systems the zero sequence voltage
increases towards the earth fault location. The inverse characteristic results in the
shortest command time for the relay closest to the fault. The other relays then reset.
Figure 2-91 Directional zero-sequence voltage time protection with non-directional backup stage
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