Rockwell Automation 20G PowerFlex 750-Series AC Drives - Manual (Page 169)

Rockwell Automation Publication 750-RM002B-EN-P - September 2013 169
Diagnostics and Protection Chapter 3
Operation of the overload is based on three parameters.
• P26 [Motor NP Amps] is the base value for motor protection.
• P413 [Mtr OL Factor] is used to adjust for the service factor of the motor.
Within the drive, motor nameplate FLA is multiplied by motor overload
factor to select the rated current for the motor thermal overload. This can
be used to raise or lower the level of current that causes the motor thermal
overload to trip without the need to adjust the motor FLA. For example, if
motor nameplate FLA is 10 Amps and motor overload factor is 1.2, then
motor thermal overload uses 12 Amps as 100%.
• P414 [Mtr OL Hertz] is used to further protect motors with limited speed
ranges. Because many motors do not have sufficient cooling ability at lower
speeds, the overload feature can be programmed to increase protection in
the lower speed areas. This parameter defines the frequency where derating
the motor overload capacity begins. For all settings of overload Hz other
than zero, the overload capacity is reduced to 70% when output frequency
is zero. During DC injection braking, the motor current can exceed 70%
of FLA, but this causes the motor overload to trip sooner than when
operating at base speed. At low frequencies, the limiting factor can be the
drive overload rather than the motor overload.
IMPORTANT Some motors have a service factor that is only for use with sine wave
(non-drive) power. Check with the motor manufacturer to see if the
nameplate service factor is valid or must be reduced when operated by
a drive.
Charging Overload Factor
% of Base Speed
Co
nt
in
uous R
atin
g
OL % = 1.20
OL % = 1.00
OL % = 0.80