Motor Overload - Allen-Bradley PowerFlex 70 Enhanced Control Reference Manual

Motor Overload

The motor overload protection feature uses an IT (inverse time) algorithm to model
the temperature of the motor and follows the same curve as a physical class 10
✔ ✔ overload device.
100000
10000
1000
100
10
100 125
[Motor NP FLA] is used by the overload feature to establish the 100% level (y axis)
shown in the graph above.
Setting the correct bit in [Fault Config x] to zero disables the motor thermal
overload. For multimotor applications (more than one motor connected to one
drive), separate external overloads for each motor are required, and the drive's
motor overload can be disabled.
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%.
Important: Some motors have a service factor that is only for use with sine
140
120
100
80
60
40
20
0 10
Motor Overload Curve
150 175 200 225
Full Load Amps (%)
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.
Changing Overload Factor
20 30 40 50 60 70 80
% of Base Speed
Motor Overload
Cold
Hot
250
OL % = 1.20
OL % = 1.00
OL % = 0.80
90 100
55