Siemens SINAMICS S 1PH7 - Motor Operates with a Periodic Duty Cycle; Periodic Duty Cycle (Example)

Configuration
2.3 Selecting and dimensioning induction motors
1PH7 induction motors (Machine tools)
Configuration Manual, (APH7W), 04/2009, 6SN1197-0AD72-0BP0
45
2.3.5 Motor operates with a periodic duty cycle
The duty cycle determines how the drive is dimensioned. It is assumed that the speeds
during the duty cycle lie below the rated speed.
If the power is known, but the torques during the duty cycle are unknown, then the power
must be converted to a torque:
M = P ∙ 9550 / n M in [Nm], P in [kW], n in [rpm]
The torque to be generated by the motor comprises the frictional torque M
friction
, the load
torque of the driven machine M
load
and the accelerating torque M
B
:
M = M
friction
+ M
load
+ M
B
The accelerating torque M
B
is calculated as follows:
0
ವ-ವ
0RWRUORDG
%

˭
-ವෙQ
0RWRUORDG
ವW
ෙQ
W
%
M
B
Acceleration torque in Nm referred to the motor shaft (on the motor side)
J
motor+load
Total moment of inertia in kgm
2
(on the motor side)
Δn Speed variation in rpm
t
B
Acceleration time, in s
0 0
 PD[F\FOH
0
7
0

W

W

0

0

W

W

W

W
0

Figure 2-2 Periodic duty cycle (example)
The M
rms
torque must be calculated from the load cycle:
0
UPV
0t෬W0t෬W
 
7
A differentiation should be made depending on the period T and the thermal time constant
T
th
of the motor that is dependent on the shaft height:
● T/T
th
≤ 0.1 (for a cycle duration of 2 to 4 min)
● 0.1 ≤ T/T
th
≤ 0.1 (for a cycle duration of 3 to 20 min)
● T/T
th
> 0.5 (for a cycle duration of approx. 15 min)