Rockwell Automation 20B PowerFlex 70, PowerFlex 700 Reference Manual - Manual (Page 117)

Motor Overload
Rockwell Automation Publication PFLEX-RM001H-EN-P - June 2013 117
Motor Overload
Also see Motor Overload Protection on page 119 .
The motor thermal overload uses an IT algorithm to model the temperature of
the motor. The curve is modeled after a Class 10 protection thermal overload
relay that produces a theoretical trip at 600% motor current in ten (10) seconds
and continuously operates at full motor current.
Motor nameplate FLA programming is used to set the overload feature. This
parameter, which is set in the start up procedure, is adjustable from 0 - 200% of
drive rating and should be set for the actual motor FLA rating.
Setting the correct bit in [Fault Config x] to zero disables the motor thermal
overload. Most multimotor applications (using one drive and more than one
motor) will require the MTO to be disabled since the drive would be unable to
distinguish each individual motor’s current and provide protection.
Operation of the overload is based on three parameters; [Motor NP FLA],
[Motor OL Factor] and [Motor OL Hertz].
1. [Motor NP FLA] is the base value for motor protection.
2. [Motor 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 will cause 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 will use 12 Amps as 100%.
Motor Overload Curve
10
100
1000
10000
100000
100 125 150 175 200 225 250
Full Load Amps (%)
Trip Time
(Seconds)
Cold
Hot