Single-Phase Overcurrent Protection
The single-phase overcurrent protection evaluates the current that is measured by the sensitive Ι
NS
- or the
normal Ι
N
input. Which input is used depends on the device version according to the order number.
Applications
•
Plain ground fault protection at a power transformer
•
Sensitive tank leakage protection.
Description
The single-phase definite time overcurrent ground protection is illustrated by the tripping characteristic as
shown in Figure 2-21. The current to be measured is filtered by numerical algorithms. Because of the high
sensitivity a particularly narrow band filter is used. The current pickup thresholds and tripping times can be
set. The detected current is compared to the pickup value 50 1Ph-1 PICKUP or 50 1Ph-2 PICKUP and
reported if this is violated. After expiry of the respective delay time 50 1Ph-1 DELAY or 50 1Ph-2 DELAY,
the trip command is issued. The two elements together form a two-stage protection. The dropout value is
approximately 95% of the pickup value for currents greater than I > 0.3 · INom.
The current filter is bypassed if currents are extremely high in order to achieve a short tripping time. This
occurs automatically as soon as the instantaneous value of the current exceeds the set value of the 50 1Ph-2
PICKUP element by at least factor 2 · √2.
[ueb-einph-kennlinie-020926-rei, 1, en_US]
Figure 2-21 Two-stage characteristic of the single-phase time-overcurrent protection
The following figure shows the logic diagram of the single-phase overcurrent protection function.
2.4
2.4.1
Functions
2.4 Single-Phase Overcurrent Protection
SIPROTEC 4, 7SJ61, Manual 77
C53000-G1140-C210-6, Edition 05.2016
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