Rockwell Automation 150 MNL/SMC DIALOG+/APP-PROD GUIDE - Manual (Page 173)

Reference 10-11
Table 10.M Motor Output - Comparison of NEMA Polyphase Designs
Calculating Torque
(Acceleration Torque
Required for Rotating Motion) Some machines must be accelerated to a given speed in a certain
period of time. The torque rating of the drive may have to be
increased to accomplish this objective. The following equation may
be used to calculate the average torque required to accelerate a known
inertia (WK
2
). This torque must be added to all the other torque
requirements of the machine when determining the drive and motor’s
required peak torque output.
Where:
T = Acceleration Torque (ft.-lb.)
WK
2
= total system inertia (ft.-lb.
2
) that the motor must accelerate. This
value includes motor armature, reducer, and load.
D N = Change in speed required (RPM
t = time to accelerate total system load (seconds).
Note: The number substituted for (WK
2
) in this equation must be in
units of ft.-lb.
2
. Consult the conversion tables for the proper
conversion factor.
NEMA
Design
Starting
Torque
Locked
Rotor
Torque
Breakdown
Torque
% Slip Applications
A High High High < 5% Broad applications including fans, blowers, pumps, and machine tools.
B Normal Normal Normal < 5%
Normal starting torque for fans, blowers, rotary pumps, unloaded
compressors, conveyors, metal cutting, machine tools, miscellaneous
machinery.
C Low High Low Low
High inertia starts such as large centrifugal blowers, fly wheels and
crusher drums. Loaded starts such as piston pumps, compressors and
conveyors.
D Normal High None
High
Very high inertia and loaded starts. Choice of slip range to match
application.
5–8% Punch press, sheers and forming machine tools.
8–13% Cranes, hoists, elevators and oil well pumping jacks.
T
WK
2 ∆
N
( ) ×
30 8t
Ч
--------------------------- =