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2 Functions
Zero Sequence
Voltage Time Pro-
tection (U
-inverse)
0
156
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 8LQY PLQLPXP, valid for t→ ∞ and in time direction by a deter-
mined constant time 7 IRUZ 8LQY ). 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
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 7 UHY 8LQY 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.
. For meshed earthed systems the zero sequence voltage
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7SA522 Manual
C53000-G1176-C155-3
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