SIEMENS
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Siemens CR 1 · 2015
7
■
Configuration
(continued)
SIMOTICS motors for cranes
General technical specifications
Calculating the rms value, ON duration
Actual duty can also be converted to a thermally equivalent
S3 mode by means of "rms value calculation", which means that
the S3 motor tables can be used again.
A torque diagram (duty cycle diagram) must be available when
the calculation is performed (see diagrams below).
The value (assumed to be constant throughout the operating
time) that would generate the same temperature rise as the ac-
tual torque is defined as the rms torque. The ON duration is the
sum of operating times with respect to the total duty cycle dura-
tion.
If the individual traveling duty cycles are not the same (e.g. due
to different loads or distances), all the different traveling cycles
must be included in the rms value and ON duration calculation
until they repeat themselves.
Differences in thermal behavior when the motor is running and
when it is at a standstill are already taken into account with res-
pect to the ON durations in the S3 tables. For this reason,
M
rms
must be calculated with respect to the operating time
t
e
and not
to the duty cycle duration
t
S
.
To ensure that the rms value can be defined with sufficient accu-
racy, however, the operating phases during which the motor is
not cooled as efficiently must be taken into account (e.g. during
correction runs at low speeds and with naturally cooled motors).
Effects such as these can only be taken into account by the mo-
tor manufacturer.
The operating conditions for hoist and traversing gears also vary
enormously:
•
The external moment of inertia with respect to the motor mo-
ment of inertia is usually greater in traversing gears than in
hoist gears; in other words, the acceleration and braking work
are more relevant for traversing gears than for hoists even
when the number of duty cycles performed and the
ON duration are the same.
•
The steady-state torque (load torque) with respect to the rated
motor torque is usually greater in hoists than in traversing ge-
ars (traveling resistance).
•
The torque diagram for traversing gears does not take the di-
rection of travel into account (without wind forces). The effect
of the payload is minimal with high traversing gear weights;
i.e. with handling cranes, it is repeated after each travel move-
ment (after the second travel movement at the latest).
•
The torque diagram for hoists is largely dependent on the
load. The motor torques when the same load is hoisted and lo-
wered are different (efficiency) and, in the case of handling
cranes, a traveling duty cycle with a load is usually followed
by a traveling duty cycle with empty load tackle (collective loa-
ding; see also FEM, Section I, Calculation Principles for Cra-
nes); i.e. the cycle required for calculating the rms value is re-
peated after the fourth travel movement at the earliest.
Torque diagram
Typical torque diagram for a gantry across one conveying cycle
Typical torque diagram for hoist across one conveying cycle
ED
ON time
M
rms
rms torque
M
1
,
M
2
,
M
3
Torques in travel diagram
t
1
,
t
2
,
t
3
Operating times of torques
M
1
,
M
2
,
M
3
t
P
Idle time
t
e
Operating time of motor =
t
1
+
t
2
+
t
3
t
S
Duty cycle duration =
t
e
+
t
P
√
M
rms
=
∑
M
2
×
t
t
e
ED =
t
e
×
100
t
S
%
G_CR01_EN_00018
M
rms
t
S
t
P
t
t
e
3
M
3
t
2
t
1
t
2
M
1
M
M
G_CR01_EN_00019
Starting torques
Braking torques
Frictional torques
M
A
M
M
Br
M
Br
M
R
M
R
M
R
M
Br
M
A
M
A
t
M
A
M
A
M
M
Br
M
Br
M
Br
t
M
H
M
S
M
H
M
S
M
A
M
A
M
Br
M
A
M
Br
M
H
M
S
G_CR01_EN_00020
Starting torques
Braking torques
Hoisting torques
Lowering torques
Lift
with load
Lower
Lower
with load
Lift
without load
without load
© Siemens AG 2015