10.2 Selection Procedure
10-4
(1) Calculating the load torque during constant speed running (For detailed calculation, refer to section
10.3.1)
It is essential to calculate the load torque during constant speed running for all loads.
First calculate the load torque of the motor during constant speed running and then select a tentative
capacity so that the continuous rated torque of the motor during constant speed running becomes higher
than the load torque. To perform capacity selection efficiently, it is necessary to match the rated speeds
(base speeds) of the motor and load. To do this, select an appropriate reduction-gear (mechanical
transmission) ratio and the number of motor poles.
If the acceleration or deceleration time is not restricted, the tentative capacity can apply as a defined
capacity.
(2) Calculating the acceleration time (For detailed calculation, refer to section 10.3.2 [ 2 ] )
When there are some specified requirements for the acceleration time, calculate it according to the following
procedure:
1) Calculate the moment of inertia for the load and motor.
Calculate the moment of inertia for the load, referring to “10.3.2 Acceleration and deceleration time
calculation.” For the moment of inertia for motors, refer to the related motor catalogs.
2) Calculate the minimum acceleration torque (See Fig. 10.2-2)
The acceleration torque is the difference between the motor short-time output torque (base frequency:
60 Hz) explained in “10.1 (2) Maximum driving torque in a short time” and the load torque (
L
/
G
)
during constant speed running calculated in the above (1) . Calculate the minimum acceleration torque
for the whole range of speed.
3) Calculate the acceleration time
Assign the value calculated above to the equation ((Equation 10.3-15) in “10.3.2 Acceleration and
deceleration time calculation” to calculate the acceleration time. If the calculated acceleration time is
longer than the expected time, select the inverter and motor having one class larger capacity and
calculate it again.
Fig. 10.2-2 Example study of minimum acceleration torque
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