Siemens SIPROTEC 4 7UT6 Series Manual page 138

Functions
2.4 Time Overcurrent Protection for Phase and Residual Currents
[logik-hochstromstufen-i-fuer-nullstrom, 1, en_GB]
Figure 2-68
Each phase current and the zero sequence current 3·Ι
(common setting for the three phase currents) and 3I0> (independent setting for 3Ι
used, a frequency analysis is performed first. Depending on the detection of inrush currents, either normal
pickup annunciations or relevant inrush messages are issued. After user-configured delay times T I> or T
3I0> have elapsed, a trip signal is issued assuming that no inrush current is detected or inrush restraint is
disabled. If inrush restraint is enabled and inrush current is detected, there will be no tripping. Nevertheless,
an annunciation is generated indicating that the time expired. Tripping signals and signals on the expiration of
time delay are available separately for each stage. The reset values are approximately 95 % below the pickup
value for settings above Ι
currents near the pickup value (e.g. 20 % at 0.2 · Ι
Figure 2-69 and
the zero sequence current stage 3I0>.
138
Logic diagram of the high-set stages I>> for residual current (simplified)
. Lower values require a higher hysteresis in order to avoid intermittent pickup on
N
Figure 2-70 show the logic diagrams for the overcurrent stages I> for phase currents and for
are, additionally, compared with the setting value I>
0
).
N
C53000-G1176-C230-5, Edition 09.2016
). If inrush restraint is
0
SIPROTEC 4, 7UT6x, Manual