Functions
2.5 Inrush Restraint
SIPROTEC, 7SD80, Manual
E50417-G1140-C474-A1, Release date 09.2011
99
Figure 2-33 Logic diagram of the cross-block function for one end
2.5.2 Setting Notes
The inrush current detection is required for the following applications:
• For the differential protection if an inductance is located in the protected zone.
• For the time overcurrent protection if a transformer is located in the protected zone or if the protected line
ends on a transformer.
Inrush current detection can be turned ON or OFF at address 2301INRUSH REST..
It is based on the evaluation of the second harmonic which exists in the inrush current. Ex-works a ratio of 15 %
of the 2nd HARMONIC I
2fN
/I
fN
is set under address 2302, which can normally be taken over. However, the com-
ponent required for restraint can be parameterized. In order to be able to achieve a higher degree of restraint
in case of exceptionally unfavorable inrush conditions, you may also set a smaller value.
However, if the local measured current exceeds a value set in address 2305 MAX INRUSH PEAK, there will
be no inrush restraint. The peak value is decisive. The set value should be higher than the maximum inrush
current peak value that can be expected. For transformers set the value above √2·I
NTransf.
/u
kTransf.
. If a line ends
on a transformer, a smaller value may be selected, considering the damping of the current by the line imped-
ance.
The crossblock function can be activated (YES or deactivated (NO) in address 2303 CROSS BLOCK. The time
after exceeding of the current threshold for which this crossblock is to be activated is set under address 2310
CROSSB 2HM. With the setting ∞ the crossblock function is always active until the second harmonic content in
all phases has dropped below the set value.
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