Setting Notes - Siemens SIPROTEC 7SJ61 Manual

Functions
2.4 Single-Phase Overcurrent Protection
2.4.4

Setting Notes

General
Single-phase time overcurrent protection can be set ON or OFF at address 2701 50 1Ph.
The settings are based on the particular application. The setting ranges depend on whether the current mea-
suring input is a sensitive or a normal input transformer (see also „Ordering Information" in Appendix A.1).
In case of a normal input transformer, set the pickup value for 50 1Ph-2 PICKUP in address 2702, the pickup
value for 50 1Ph-1 PICKUP in address 2705. If only one element is required, set the one not required to ∞.
In case of a sensitive input transformer, set the pickup value for 50 1Ph-2 PICKUP in address 2703, the
pickup value for 50 1Ph-1 PICKUP in address 2706. If only one element is required, set the one not required
to ∞.
If you need a tripping time delay for the50-2 elements,set it in address 2704 50 1Ph-2 DELAY, for the 50-1
element in address 2707 50 1Ph-1 DELAY. With setting 0 s no delay takes place.
The selected times are additional time delays and do not include the operating time (measuring time, etc.) of
the elements. The delay can also be set to ∞; the corresponding element will then not trip after pickup, but the
pickup is reported.
Special notes are given in the following for the use as high-impedance unit protection and tank leakage protec-
tion.
Application as High-impedance Protection
The application as high-impedance protection requires that starpoint current detection is possible in the system
in addition to phase current detection (see example in Figure 2-23). Furthermore, a sensitive input transformer
must be available at device input I
tion is set at the 7SJ61 device for the current at input I
The entire function of high-impedance protection is, however, dependent on the interaction of current trans-
former characteristics, external resistor R and voltage across R. The following section gives information on this
topic.
Current Transformer Data for High-impedance Protection
All current transformers must have an identical transformation ratio and nearly equal knee-point voltage. This
is usually the case if they are of equal design and identical rated data. The knee-point voltage can be approx-
imately calculated from the rated data of a CT as follows:
V Knee-point voltage
KPV
R Internal burden of the CT
I
P Nominal power of the CT
Nom
I Secondary nominal current of CT
Nom
ALF Rated accuracy limit factor of the CT
88
/I . In this case, only the pickup value for single-phase overcurrent protec-
N NS
/I .
N NS
SIPROTEC, 7SJ61, Manual
C53000-G1140-C210-1, Release date 02.2008