Siemens SIPROTEC 4 7SJ61 Manual page 199

The ΣΙ method does not feature integrated threshold evaluation. But using CFC it is possible to implement a
threshold, which logically combines and evaluates the three summation currents via an OR operation. Once
the summation current exceeds the threshold, a corresponding message will be triggered.
ΣΙ x -Procedure
While the ΣΙ-procedure is always enabled and active, use of the ΣI
configuration. This procedure operates analogously to the ΣΙ-procedure. The differences relate to the involu-
tion of the tripping currents and their reference to the exponentiated rated operating current of the CB. Due to
the reference to Ι
CB manufacturer. The displayed values can be interpreted as the number of trips at rated operational current
of the CB. They are displayed in the statistics values without unit and with two decimal places.
The tripping currents used for calculation are a result of the rms values of the fundamental harmonic, which is
recalculated each cycle.
If the start criterion is satisfied (as described in Section „General"), the r.m.s. values, which are relevant after
expiration of the opening time, are checked for each phase as to whether they comply with the current crite-
rion. If one of the values does not satisfy the criterion, its predecessor will be used instead for calculation. If no
r.m.s. value satisfies the criterion up to the predecessor of the starting point, which is marked by the start
criterion, a trip has taken place which only affects the mechanical lifetime of the breaker and is consequently
not detected by this procedure.
If the current criterion grants the logic release after the opening time has elapsed, the recent primary tripping
currents (Ι ) are involuted and related to the exponentiated rated operating current of the CB. These values
b
are then added to the existing statistic values of the ΣΙ
started using threshold
one of the new statistic values lies above the threshold, the message
2P-Procedure
The application of the two-point procedure for the calculation of the remaining lifespan depends on the CMD
configuration. The data supplied by the CB manufacturer is transformed in such manner that, by means of
measuring the fault currents, a concrete statement can be made with regard to the still possible operating
cycles. The CB manufacturer's double-log operating cycle diagrams form the basis of the measured fault
currents at the time of contact separation. Determination of the fault currents is effected in accordance with
the method as described in the above section of the ΣΙ
The three results of the calculated remaining lifetime are represented as statistic value. The results represent
the number of still possible trips, if the tripping takes place when the current reaches the rated operational
current. They are displayed without unit and without decimals.
As with the other procedures, a threshold logically combines the three "remaining lifetime results" via an OR
operation and evaluates them. It forms the "lower threshold", since the remaining lifetime is decremented
with each trip by the corresponding number of operating cycles. If one of the three phase values drops below
the threshold, a corresponding message will be triggered.
A double-logarithmic diagram provided by the CB manufacturer illustrates the relationship of operating cycles
and tripping current (see example in
determined (for tripping with equal tripping current). According to the example, approximately 1000 trips can
yet be carried out at a tripping current of 10 kA. The characteristic is determined by two vertices and their
connecting line. Point P1 is determined by the number of permitted operating cycles at rated operating
current Ιr, point P2 by the maximum number of operating cycles at rated fault tripping current Ιsc. The associ-
ated four values can be configured.
SIPROTEC 4, 7SJ61, Manual
C53000-G1140-C210-6, Edition 05.2016
x , the result is an approximation to the number of make-break operations specified by the
r
ΣI^x> as well as the output of the new related summation tripping current powers. If
Figure 2-77). This diagram allows the number of yet possible trips to be
x -procedure depends on the CB maintenance
x -procedure. Subsequently, threshold comparison is
Threshold ΣI^x> is generated.
x –procedure.
Functions
2.17 Auxiliary Functions
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