Functions
2.18 Auxiliary Functions
SIPROTEC, 7SK80, Manual
E50417-G1140-C344-A4, Release date 08.2010
250
Figure 2-96 Value limitation of directional coefficient
If the current criterion described in the Section „General“ grants the phase-selective logic release, the present
number of operating cycles is calculated based on the tripping currents determined when the CB operating time
on tripping has elapsed. They are set off against the remaining lifetime allowing the present statistic values to
be displayed and the evaluation to be started using the specified threshold. If one of the new values lies above
the threshold, the message „Thresh.R.Endu.<“ is generated.
Three additional phase-selective statistic values are provided to determine the portion of purely mechanical
trips among the results of the remaining lifetime (e.g. for phase A: „mechan.TRIP A=“). They act as counters
which count only the trips whose tripping currents are below the value of the current criterion.
I
2
t-Procedure
During the I
2
t-procedure the squared fault current integral occurring per trip is added up phase-selectively. The
integral is derived from the squared instantaneous values of the currents occurring during arc time of the circuit
breaker. This results in:
T CB arc = (parameter 266 T 52 BREAKTIME) – (parameter 267 T 52 OPENING).
The three sums of the calculated integrals are represented as statistic values referred to the squared device
nominal current (I
nom
2
). As with the other procedures, a threshold logically combines the three sums via an OR
operation and evaluates them.
The calculated squared tripping currrent integrals are added to the existing statistic values. Subsequently,
threshold comparison is started using threshold „ΣI^2t>“, and the new statistic values are output. If one of
the values lies above the threshold, the message „Thresh. ΣI^2t>“ is generated.
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