Motor Overload - Allen-Bradley PowerFlex 70 Reference Manual

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Motor Overload

Motor Overload
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.
100000
10000
1000
100
10
100 125
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
150 175 200 225
Full Load Amps (%)
Cold
Hot
250