SIEMENS
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Siemens CR 1 · 2015
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Configuration
(continued)
SIMOTICS motors for cranes
General technical specifications
Intermittent duty without the effect of the start-up
process (S3)
Definition
Operation that involves a sequence of similar duty cycles, each
with a constant-load period and idle time, whereby the starting
current does not have a noticeable effect on the temperature rise
(the duty cycle duration is generally short enough to ensure that
thermal equilibrium is not attained).
Explanation
The operating time
t
e
must be less than 3 ×
T
L
to ensure that the
theoretical final temperature
ϑ
e
is not reached. The subsequent
idle time
t
p
, however, is also less than 3 ×
T
St
, which means that
the ambient temperature is no longer reached. A mean
steady-state value
ϑ
mean
develops around which the tempera-
ture varies, but is below the theoretical final temperature
ϑ
e
.
The rated motor output during intermittent duty is greater than
during continuous duty. The time constants
T
L
and
T
St
may be
different. This influences the rated output during intermittent duty
and is taken into account in the S3 motor tables.
To determine the most suitable motor, therefore, a knowledge of
the operating and idle times is required in addition to the requi-
red output during the operating time. They are specified by the
duty cycle duration (total time) and the relative ON duration in %
of the cycle duration. If no data has been provided for the duty
cycle duration, 10 minutes apply in accordance with
DIN EN 60034-1. The S3 motor tables are based on this. Values
of 15, 25, 40, and 60 % are recommended for the cyclic duration
factor.
Effect of varying duty cycle durations
The S3 rated output is designed in such a way that the tempera-
ture peaks
ϑ
max
match the permissible values with a 10 minute
duty cycle duration (see "a" in diagram below). Shorter duty
cycle durations are not critical because lower temperature
peaks occur at the same mean winding temperature
ϑ
mean
(see "b" in diagram below). Since longer duty cycle durations
result in higher temperature peaks (see "c" in diagram below)
which, in turn, reduce the service life of the insulation, advice
from a third party should be sought in this case.
In S3 duty, the start-up processes are not discounted; the rele-
vant standard assumes that they do not have any significant in-
fluence on the temperature rise. Any number of duty cycles can
be carried out per hour provided that this standard is fulfilled.
P
t
P
V
t
t
e
max.
<
t
e
3
T
.
L
<
t
P
3
T
.
St
t
e
t
P
t
S
G_CR01_EN_00014
mean
G_CR01_EN_00015
mean
minutes
max.
t
a
b
c
10
max.a
max.b
max.c
t
Sa
t
Sb
t
Sa
t
Sb
t
Sc
t
Sc
<
<
<
<
=
10 min
max.b
max.a
max.c
© Siemens AG 2015