ilable torque will
be more and in others less.
NEMA defines the minimum starting torque or locked rotor torque
requirements and breakdown torque requirements for each NEMA
design and horsepower rating. A graph of the minimum torque is
shown for operation across-the-line (see graph). Minimum locked
rotor torque is equal to or greater than 150%, as a minimum, 30
HP and below and less than 150% above 30 HP. Breakdown or
peak torque is over 175% through 500 HP.
When a controller with 150% current capability is applied to a
motor, up to 150% torque is typically available for starting and
peak torque requirements. Compared to operation across-the-line,
this would result in less starting torque through 30 HP. The peak
torque available would be limited to 150% which would be less
than the minimum NEMA required breakdown torque.
A good estimate of available torque and corresponding current
requirements for operation between 6 and 60 Hz, can be deter-
mined by referring to the performance data provided in the action
guide and assuming that current is proportional to torque through
150%. (125% if the maximum controller current is 125%). This
highlights the importance of understanding the load torque
requirements when applying a controller to an application that has
been operated at fixed speed.
NOTE:
This material is not intended to provide operational
instructions. Appropriate Reliance Electric instruction manuals
and precautions should be studied prior to installation, operation
or maintenance of equipment.
Introduction
Application Solution
NEMA Minimum Torque
800 RPM - Design B Motors Reach us now at www.rockwellautomation.com
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Publication D-7729 March 2000
© 2000 Rockwell International Corporation All Rights Reserved Printed in USA
NOTE: This material is not intended to provide operational instructions. Appropriate Reliance
Electric Drives instruction manuals precautions should be studied prior to installation,
operation, or maintenance of equipment.