Single-Phase Overcurrent Protection; Functional Description - Siemens siprotec SJ62 User Manual

2 Functions
2.5

Single-Phase Overcurrent Protection

Applications
2.5.1

Functional Description

123
The single-phase overcurrent protection evaluates the current that is measured by the
sensitive I - or the normal I
NS
version and the order number.
• Plain ground fault protection at a power transformer;
• Sensitive tank leakage protection.
The single-phase time overcurrent function yields the tripping characteristic depicted
in Figure 2-35. Numerical algorithms filter the current to be detected. A particular
narrow-band filter is used due to the possible high sensitivity. 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 violat-
ed. The trip command is generated after the associated delay time 50 1Ph-1 DELAY
or 50 1Ph-2 DELAY has elapsed. The two elements together form a two-stage pro-
tection. The dropout value is roughly equal to 95% of the pickup value for currents I >
0.3 · I .
Nom
The current filter is bypassed if currents are extremely high to achieve a short tripping
time. This will always happen automatically when the instantaneous current value
exceeds the setting value of the 50 1Ph-2 PICKUP element by at least factor 2 · √2.
Figure 2-35 Two-stage characteristic of the single-phase time-overcurrent protection
input. Which transformer is used depends on the device
N
SIPROTEC 4, 7SJ62/63/64 Handbuch
C53000-G1140-C147-A, Edition 07.2015