Functions
2.4 Single-Phase Overcurrent Protection
SIPROTEC, 7SJ61, Manual
C53000-G1140-C210-1, Release date 02.2008
88
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
N
/
I
NS
. In this case, only the pickup value for single-phase overcurrent protec-
tion is set at the 7SJ61 device for the current at input
I
N
/
I
NS
.
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
KPV
Knee-point voltage
R
I
Internal burden of the CT
P
Nom
Nominal power of the CT
I
Nom
Secondary nominal current of CT
ALF
Rated accuracy limit factor of the CT