Motor Overload - Allen-Bradley PowerFlex 753 Quick Start Manual

Reference Section

Motor Overload

It can be necessary to adjust parameter 414 [Mtr OL Hertz]. Adjusting this parameter to a default of 20 Hz is a conservative
setting to protect a typical induction motor that is not designed to adequately cool itself at full load when its rotor/internal
fan is turning less than 20 Hz. Understand the speed range specifications of your motor in order to set parameter 414
[Mtr OL Hertz] to the approximate minimum operating speed under full load.
Motor and drive applications operate on a wide variety of operating speed ranges. Typical speed ratios for constant and
variable torque motors in applications are expressed in terms of Motor Base Speed to Motor Minimum Speed.
Refer to Table 55.
Table 55 - Typical Speed Ratios for Constant and Variable Torque Motors
Example Motor Base Speed = 1750 RPM / 60 Hz
Minimum Speed
RPM Hz % Motor Base Speed Speed Range Ratio
875 30
438 15
175 6
88 3
17.5 0.6
1.8 0.06 0.1
82
50 2:1
25 4:1
10 10:1
5 20:1
1 100:1
1000:1
Rockwell Automation Publication 750-QS001A-EN-P - March 2015