Functions
2.17 Auxiliary Functions
SIPROTEC, 7SJ61, Manual
C53000-G1140-C210-1, Release date 02.2008
220
Σ
I
-Procedure
Being a basic function, the
Σ
I
-procedure is unaffected by the configuration and does not require any procedu-
respecific settings. All tripping currents occurring 1½ periods after a protective trip, are summed up for each
phase. These tripping currents are r.m.s. values of the fundamental harmonic.
The interrupted current in each pole is determined for each trip signal. The interrupted fault current is indicated
in the fault messages and is added up with previously stored fault current values in the statistic-counters. Mea-
sured values are indicated in primary terms.
The
Σ
I
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.
Σ
I
x
Procedure
While the
Σ
I
-procedure is always enabled and active, use of the
Σ
I
x
-procedure depends on the CB mainte-
nance configuration. This procedure operates analogously to the
Σ
I
-procedure. The differences relate to the
involution of the tripping currents and their reference to the exponentiated rated operating current of the CB.
Due to the reference to
I
r
x
, the result is an approximation to the number of make-break operations specified by
the 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 criterion.
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 (
I
b
) are involuted and related to the exponentiated rated operating current of the CB. These values are
then added to the existing statistic values of the
Σ
I
x
-procedure. Subsequently, threshold comparison is started
using threshold
„
Σ
I^x>“
as well as the output of the new related summation tripping current powers. If one of
the new statistic values lies above the threshold, the message
„Threshold
Σ
I^x>“
is generated.
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 mea-
suring 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
Σ
I
x
–procedure.
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 cur-
rent. 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.