Selection criteria
SELECTING CRITERIA
Asynchronous motor selection
5.
· 187 ·
Ref.2003
QC-PDS
HARDWARE
5.3.2 Calculation of acceleration and braking time
After selecting the mechanical characteristics and the power of the drive,
the acceleration and braking time is calculated as follows:
5.3.3 Calculation of power with intermittent load
Forming the drive to the right dimensions has to be done with the greatest
care when the application involves a periodical starting and stopping
operation, frequently repeated as in the case of threading with a miller.
For a cycle like the one shown in figure F. H5/11, which includes acceleration
and stopping, the equivalent effective torque T
R
of the equation must be
within the S1 dimension given for the drive torque.
Calculations:
1. When the speed ranges from 0 to 1 500 rpm.
2. When the speed ranges from 0 to 6 000 rpm.
P
N
2
60
-------
2
J
M
N
M
2
1000t
---------------------- k W
2
60
-------
2
0.13 1500
2
1000 0.5
---------------------------------
6.41 kW 1===
P
N
2
60
-------
2
J
M
N
M
2
N
B
2
+
2000t
-------------------------------------- k W
2
60
-------
2
0.13 6000
2
1500
2
+
2000 2.5
--------------------------------------------------------
10.89 kW2===
Constant torque
area:
(0 < N
M
< N
B
)
Constant power
area:
(N
B
< N
M
< N
max
)
Constant torque &
power area:
(N
B
< N
M
< N
max
)
J
M
Inertia of the load in kg·m² with regard to the motor shaft
T
M
Rated torque at base speed in N·m
N
max
Maximum motor speed in rpm
N
B
Motor base speed in rpm
N
M
Motor speed reached after a time period t in rpm
t
1
2 J
M
N
M
60 T
M
------------------------------- s=
t
2
2 J
M
N
M
2
N
B
2
–
120 T
M
N
B
-----------------------------------------------------s=
t
3
t
1
t
2
+
2 J
M
N
M
2
N
B
2
+
120 T
M
N
B
--------------------------------------------------- s==
F. H5/11
Periodic start-stop operation.
0
speed
0
torque
Tc
time
Nm
TL
Tp
-Tp
Tr TfTs
time
T
R
T
P
2
t
r
t
f
+ T
L
2
t
s
+
t
c
-------------------------------------------------------
Nm=
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