Functions
6.6 Calculating switching cycles
Motor
starter (3RK1308‑0**00‑0CP0)
Equipment Manual, 11/2019, A5E34821005002A/RS-AC/003
85
Switching cycle parameters
The following table shows all the parameters that you have to consider for calculation of the
permissible switching cycle:
Parameters
Description
Conditions
Starting time
t
Startup
[s]
Time during which the motor
accelerates up to its operating
speed from standstill
The maximum is determined by the
parameterized tripping class and the intrinsic
device protection (see also Overload protection
(Page 76)).
Starting current
I
Startup
[A]
Root-mean-square of the motor
current that flows during the
starting time. It is considered as a
multiple x of the rated value of the
motor I
rated_motor
or of the
parameterized rated operational
current I
e
.
I
Startup
[A] = x * I
e
[A]
The maximum is the permissible current of the
relevant device class. Consider additional idle
times in the case of starting currents in excess
of 65 A (see example graphics).
(Also see: Overload protection (Page 76) and
the example graphics)
Motor operation time t
Motor
[s]
Time in which the motor is in
operation after startup.
-
Rated operational
current
I
e
[A]
Root-mean-square of the motor
current in the operating phase after
the starting time or the
parameterized value I
e
of the
motor starter
The permissible I
e
is determined by the
adjustment range of the motor starter used and
its ambient temperature (see also:
Overload protection (Page 76)).
Motor OFF time:
t
Off
[s]
Idle time of the motor within the
switching cycle
Consider additional idle times in the case of
starting currents in excess of 65 A
(see example graphics).
Switching cycle
interval
T [s]
Total of t
Off,
t
Motor
and t
Startup
The maximum time is 300 s.
You use the switching cycle interval time to determine the permissible starting frequency per
hour as follows:
