Siemens siprotec SJ62 User Manual page 326

Σ I-Procedure
Σ I
x
Procedure
2P-Procedure
SIPROTEC 4, 7SJ62/63/64 Handbuch
C53000-G1140-C147-A, Edition 07.2015
Being a basic function, the ΣI-procedure is unaffected by the configuration and does
not require any procedure-specific settings. All tripping currents occurring 1
after a protective trip, are summed up for each phase. These tripping currents are rms
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. Measured values are indicated in primary
terms.
The ΣI 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.
While the ΣI-procedure is always enabled and active, use of the ΣI
depends on the CB maintenance configuration. This procedure operates analogously
to the ΣI-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 ref-
x
erence to I , the result is an approximation to the number of make-break operations
r
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 sta-
tistics values without unit and with two decimal places.
The tripping currents used for calculation are a result of the rms values of the funda-
mental harmonic, which is recalculated each cycle.
If the start criterion is satisfied (as described in Section „General"), the rms 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 rms value satis-
fies the criterion until 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
rated operating current of the CB. These values are then added to the existing statistic
values of the ΣI
x
-procedure. Subsequently, threshold comparison is started using
threshold „ΣI^x>", and the new related summation tripping current powers are
output. If one of the new statistic values lies above the threshold, the message
„Threshold ΣI^x>" is generated.
Availability of the two-point procedure for calculating the remaining lifetime depends
on the CBM configuration. The data supplied by the CB manufacturer are thus con-
verted that measurement of the tripping currents allows a reliable statement to be
made concerning the still possible make-break operations. This is based on the
double-logarithmic operating cycles diagrams of the CB manufacturers and the trip-
ping currents measured the moment the poles part. The tripping currents are deter-
mined analogously to the method described previously for the ΣI
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 life-
time results" via an OR operation and evaluates them. It forms the „lower threshold",
) are involuted and related to the exponentiated
b
2.23 Auxiliary Functions
1
/ periods
2
x
-procedure
x
-procedure.
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