Siemens siprotec SJ62 User Manual page 90

SIPROTEC 4, 7SJ62/63/64 Handbuch
C53000-G1140-C147-A, Edition 07.2015
Figure 2-17 Overcurrent protection for parallel transformers
For line sections supplied from two sources or in ring-operated lines the time overcur-
rent protection has to be supplemented by the directional criterion. Figure 2-18 shows
a ring system where both energy sources are merged to one single source.
Figure 2-18 Transmission lines with sources at each end
Depending on the setting of parameter 613 Gnd O/Cprot. w., the ground current
element can operate either with measured values I
from the three phase currents. Devices featuring a sensitive ground current input,
however, use the calculated quantity 3I0.
For each element the time can be blocked via binary input or automatic reclosure
(cycle-dependent), thus suppressing the trip command. Removal of blocking during
pickup will restart time delays. The Manual Close signal is an exception. If a circuit
breaker is manually closed onto a fault, it can be re-opened immediately. For overcur-
2.3 Directional Overcurrent Protection 67, 67N
or with the values 3I0 calculated
N
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