2 Functions
156
7SA522 Manual
C53000-G1176-C155-3
Zero Sequence
Voltage Time Pro-
tection (U
0
-inverse)
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.t
The voltage/time characteristic can be displaced in voltage direction for a determined
constant voltage 8LQYPLQLPXP, valid for t→ ∞ and in time direction by a deter-
mined constant time 7IRUZ8LQY). The characteristics are shown in the Tech-
nical Data.
Figure 2-66 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.
A further time stage 7UHY8LQY provokes non-directional tripping with a
voltage-independent delay. This stage can be set above the directional stage. When
tripping with this stage it is, however, a prerequisite that the time of the voltage-con-
trolled stage has already expired (without directional check). In case the zero voltage
is too low or the voltage transformer circuit-breaker is tripped, this stage is also dis-
abled.
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