Functions
2.5 Single-Phase Overcurrent Protection
SIPROTEC, 7SJ62/64, Manual
C53000-G1140-C207-2, Release date 01.2008
129
2.5
Single-Phase Overcurrent Protection
The single-phase overcurrent protection evaluates the current that is measured by the sensitive
I
NS
- or the
normal
I
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.
2.5.1
Functional Description
The single-phase definite time overcurrent ground protection is illustrated by the tripping characteristic as
shown in Figure 2-37. The current to be measured is filtered by numerical algorithms. Because of the high sen-
sitivity 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 approximate-
ly 95% of the pickup value for currents greater than
I
> 0.3 ·
I
Nom
.
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.
Figure 2-37
Two-stage characteristic of the single-phase time-overcurrent protection
www
. ElectricalPartManuals
. com