Siemens SIPROTEC 7ST6, Руководство пользователя, Страница: 162 / 356

2 Functions
162
7ST6 Manual
E50417-G1176-C251-A3
The general straight-line equation for the double-log diagram can be derived from the
exponential function, from which the coefficients b and m can be derived.
Note
As the directional coefficient of m < -4 is technically not relevant, but can nevertheless
be derived from an incorrect parameterisation, it is limited to -4. Should the derived
coefficient fall below -4, the exponential function in the operating cycle diagram is de-
activated and, i.e. within its defined fault current range, the maximum number of oper-
ating cycles for
I
sc (
263 OP.CYCLES Isc
) is considered as a calculation result of
current operating cycles, see figure 2-46.
Figure 2-46 Value Limitation by the Direction Coefficient
If the start release is now given by the criteria as described in section "Initiation" and
the current criterion is fulfilled at the same time after expiry of the operating time on
tripping, the actual fault current is calculated (for the AT system: the fault currents), the
breaker load is determined in accordance with the method as described above and the
remaining lifespan is thus calculated. It will be displayed as a current statistical value
and additionally compared with the set limit value. Should it fall below the set limit
value, the indiciation
„Thresh.R.Endu.<“
(FNo. 16010) is generated.
All trips during which the fault current fell below the value of the current criterion (see
section "Initiation") are interpreted as purely mechanical trips and are not included in
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