Siemens siprotec SJ62 User Manual page 329

2 Functions
2
t-Procedure
I
Commissioning
327
The index i characterizes the actual tripping. With the ratio of the maximum number of
switching cycles (n
max
you get the ratio of these concerning the maximum number of possible switching
cycles in case of a tripping with rated operating current (I
In the following example, the circuit breaker has tripped 100 times with rated operating
current, 2 times with rated short-circuit current, and 3 times with 10 kA.
The number of permissible trippings with rated operating current is calculated as fol-
lowing:
RLT = Remaining lifetime
In the example, 9465 more trippings with rated operating current are possible.
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 trip-
ping 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 dis-
played 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 trip-
ping currents are below the value of the current criterion.
2
The I t-procedure depends on the CBM configuration and is only implemented in the
7SJ64. The squared tripping current integral is summated phase-selectively. The inte-
gral is calculated by means of the instantaneous values of the currents present during
CB arcing time. This yields:
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
old 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.
No measures are usually required for commissioning. If the protective relay is re-
placed (i.e. old CB and new protective relay), the initial values of the limit and statistic
values must be determined by means of a switching statistics of the CB in question.
is n at I ) to the actual calculated number of switching cycles,
r
2
). As with the other procedures, a thresh-
nom
).
r
SIPROTEC 4, 7SJ62/63/64 Handbuch
C53000-G1140-C147-A, Edition 07.2015