2.9 Backup Time Overcurrent Protection
99
7SD610 Manual
C53000-G1176-C145-4
Directional
Characteristic
The directional characteristic of the directional overcurrent stages is preset. From the
voltage and current vectors used for direction determination the angle difference
Ï•(U
)-Ï•(I) is calculated via the impedance Z Z = U/I, and the direction determined
using the displayed directional characteristic.
Figure 2-37 Directional characteristic of the time overcurrent protection
Definite Time High-
set Current Stage
I>>
Each phase current is compared with the setting value Iph>> after numerical filtering;
the earth current is compared with 3I0>> PICKUP. Currents above the associated
pickup value are detected and signalled. After expiry of the associated time delays T
Iph>> or T 3I0>> a trip command is issued. The dropout value is approximately 7%
below pickup value, but at least 1.8% of the nominal current, below the pickup value.
Figure 2-38 shows the logic diagram of the I>> stages. The stages can be blocked via
the binary input „>BLOCK O/C I>>“. Additionally, the earth current can be blocked
separately via a binary input „>BLOCK O/C Ie>>“. During the single-pole pause, the
earth current stage is always blocked to avoid a fault trigger.
The binary input „>O/C InstTRIP“ and the evaluation of the indication „switch“
(onto fault) are common to all stages and described below. They may, however, sep-
arately affect the phase and/or earth current stages. This can be achieved with two
parameters:
• I>> Telep/BI (address 2614), determines whether a non-delayed trip of this
stage via binary input „>O/C InstTRIP“ is possible (YES) or impossible (NO). This
parameter is also used for instantaneous tripping before automatic reclosure.
• I>> SOTF (address 2615), determines whether this stage shall issue non-delayed
tripping (YES) or not (NO) in case of switching-onto-fault conditions.
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