Functions
2.4 Single-Phase Overcurrent Protection
SIPROTEC, 7SJ61, Manual
C53000-G1140-C210-1, Release date 02.2008
92
If performance makes it necessary to switch several varistors in parallel, preference should by given to types
with a flat characteristic to avoid asymmetrical loading. therefore recommend the following types from
METROSIL:
600A/S1/S256 (k = 450, β = 0.25)
600A/S1/S1088 (k = 900, β = 0.25)
The pickup value (0.1 A or 0.05 A in the example) is set in address 2706 50 1Ph-1 PICKUP in the device.
The 50-2 element is not required (address 2703 50 1Ph-2 PICKUP = ∞ ).
The trip command of the protection can be delayed via address 2707 50 1Ph-1 DELAY. Normally, such delay
is set to 0.
If a higher number of CTs is connected in parallel, e.g. as busbar protection with several feeders, the magne-
tizing currents of the transformers connected in parallel cannot be neglected anymore. In this case, the mag-
netizing currents at half the knee-point voltage (corresponds to the setting value) have to be summed up. These
magnetizing currents reduce the current through the resistor R. Therefore the actual pickup value will be cor-
respondingly higher.
Application as Tank Leakage Protection
The use as tank leakage protection requires that a sensitive input transformer is available at the device input
I
N
/I
NS
. In this case, only the pickup value for single phase overcurrent protection is set at the 7SJ61 device for
the current at input I
N
/I
NS
.
The tank leakage protection is a sensitive overcurrent protection which detects the leakage current between
the isolated transformer tank and ground. Its sensitivity is set in address 2706 50 1Ph-1 PICKUP. The 50-2
element is not required (address 2703 50 1Ph-2 PICKUP = ∞ ).
The trip command of the element can be delayed in address 2707 50 1Ph-1 DELAY. It is normally set to 0.
Note
In the following settings, addresses 2703 and 2706 are valid for a highly sensitive current measuring input in-
dependently of the nominal current.
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