Functions
2.17 Auxiliary Functions
SIPROTEC, 7SJ61, Manual
C53000-G1140-C210-1, Release date 02.2008
223
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
„
Σ
I^2t>“
, and the new statistic values are output. If one of
the values lies above the threshold, the message
„Thresh.
Σ
I^2t>“
is generated.
Commissioning
Usually, no measures are required for commissioning. However, should the protection device be exchanged
(e.g. old circuit breaker and a new protection device), the initial values of the respective limit or statistical values
must be determined via the switching statistics of the respective circuit breaker.
2.17.2.3 Motor Statistics
General
There are two different types of statistical motor data:
• Operational information and
• startup information.
The statistical operational information contains the
• total number of motor startups
• total number of the motor operating hours (including startup conditions)
• total number of motor shutdown hours
For every motor startup
• the duration
• the startup current
Motor Operation Information
The motor operation statistic is newly calculated in a 600 ms cycle. In the statistics buffer, its image is de-
creased to a resolution of one hour.
Motor Startup Information
The motor startup current is displayed as a primary value. The measurement of this statistical value is initiated
upon energization of the motor. This is recognized as soon as the threshold value of the circuit breaker position
detection (parameter
212
BkrClosed I MIN
) is exceeded in at least one phase. A requirement for this is that
all three phase currents were previously below the configured threshold value.
The end of the startup time measurement is triggered as soon as the largest of the three phase currents un-
dershoots the startup current as set in parameter
1107
I MOTOR START
for at least 300 ms.
If the motor startup current (parameter
1107
I MOTOR START
) is not exceeded after energization detection
or if the current falls below the motor startup current within 500 ms after energization detection, then this is not
considered being a motor startup. No statistic is created.