2 Functions
270
7SD5 Manual
C53000-G1176-C169-1
= Not connected, see Section 2.1.2), the device will calculate the residual current
from the phase currents. Of course, all three phase currents deriving from three star-
connected current transformers must be available and connected in this case.
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 5%
below pickup value, but at least 1.5% of the nominal current, below the pickup value.
Figure 2-117 shows the logic diagram of the I>> stages. The stages can be blocked
via a binary input „>BLOCK O/C I>>“. In addition, the earth current stage can be
blocked separately via the binary input „>BLOCK O/CIe>>>“, e.g. during a single-
pole dead time before reclosure in order to avoid a spurious tripping with the zero
phase-sequence system which is present then.
Binary inputs „>O/C InstTRIP“ and the function block „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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