Single-Phase Time Overcurrent Protection; Function Description - Siemens SIPROTEC 7UT613 series Manual

2 Functions
2.7

Single-Phase Time Overcurrent Protection

2.7.1

Function Description

196
The single-phase time overcurrent protection can be assigned to either of the single-
phase measured additional current inputs of the device. This may be a „normal" input
or a high-sensitivity input. In the latter case, a very sensitive pickup threshold is pos-
sible (smallest setting 3 mA at the current input).
The single-phase time overcurrent protection comprises two definite time delayed
stages which can be combined as desired. If only one stage is required, set the other
to ∞.
Examples for application are high-impedance differential protection or high-sensitivity
tank leakage protection. These applications are covered in the following subsections.
The measured current is filtered by numerical algorithms. Due to high sensitivity, a
particularly narrow band filter is used.
For the single-phase I>>-stage, the current measured at the assigned current input is
compared with the setting value 1Phase I>>. Current above the pickup value is de-
tected and annunciated. When the delay time T I>> has expired, tripping command
is issued. The reset value is approximately 95 % of the pickup value for currents above
I
. For lower values the dropout ratio is reduced in order to avoid intermittent pickup
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on currents near the setting value (e.g. 90 % at 0.2 · I
When high fault current occurs, the current filter can be bypassed in order to achieve
a very short tripping time. This is automatically done when the instantaneous value of
the current exceeds the set value I>> stage by at least factor 2 · √2 .
For the single-phase I>-stage, the current measured at the assigned current input is
compared with the setting value 1Phase I>. Current above the pickup value is de-
tected and annunciated. When the delay time T I> has expired, the tripping command
is issued. The reset value is approximately 95 % of the pickup value for currents above
I
. Lower values require a higher hysteresis in order to avoid intermittent pickup on
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currents near the pickup value (e.g. 80 % at 0.1 · I
Both stages form a two-stage definite time overcurrent protection (figure 2-84).
Figure 2-85 illustrates the logic diagram for the single-phase overcurrent stage
).
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).
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7UT613/63x Manual
C53000-G1176-C160-2