Fagor QC-PDS - Page 186

 Selection criteria
5.
SELECTING CRITERIA
Asynchronous motor selection
· 186 ·
198
Ref.2003
QC-PDS
HARDWARE
 Limited acceleration and choke. Choke = ( acceleration /  t).
The capability demanded from the motor is determined by the following
formulas:
We will now give several examples of calculations using a mechanical
specifications and for a standard motor. The results could vary from real
ones through mechanical losses, fluctuations in mains voltage, or
inaccuracies of mechanical data.
T. H5/6 Different accelerations depending on speed.
Method Different accelerations depending on speed
Control
Linear acceleration avoiding abrupt variations in
transmitted torque.
Comment
Emulation of the square sine function for speed by
using ramps.
F. H5/10
Acceleration and choke limit.
T. H5/7 Acceleration and choke limit.
Method Acceleration and choke limit.
Control
Progressive linear acceleration, avoiding abrupt
variations of transmitted torque.
Comment
Approach square sine function (bell shape) for the
speed.
Capacity required by the motor
in the constant torque area:
(0 < N
M
< N
B
)
Capacity required by the motor
in the constant torque and
constant power area:
(0 < N
M
< N
máx
)
J
M
Inertia of the load in kg·m
2
as viewed from the motor shaft
P
N
Rated power at base speed kW
Nmax
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
Acceleration time until N
M
(in seconds) is reached
Sample
Data:
Acceleration time:
From 0 to 1500 rpm in 0.5 s (1)
From 0 to 6000 rpm in 2.5 s (2)
Motor inertia: J
motor
= 0.13 kg·m²
Motor base speed: N
b
= 1500 rpm
t i m e
s p e e d
a d j u s t s
0
P
N
2
60
------


2
J
M
N
M
2

1000 t
--------------------kW=
P
N
2
60
------


2
J
M
N
M
2
N
B
2
+
2000 t
---------------------------------------kW=