Functions
2.9 Backup Time Overcurrent Protection
SIPROTEC, 7SD610, Manual
C53000-G1176-C145-6, Release date 02.2011
102
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
= U/I and the direction determined based on the directional characteristic displayed.
Figure 2-38 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 com-
pared with 3I0>> PICKUP. After pickup of a stage and expiry of the associated delay times T Iph>> or T
3I0>> a trip command is issued. The dropout value is approximately 7% below the pickup value, but at least
1.8% of the nominal current.
Figure 2-39 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 pickup.
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, separately 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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