Motor Overload - Allen-Bradley powerflex 700 User Manual

Appendix C Application Notes

Motor Overload

122
For single motor applications the drive can be programmed to protect the motor
from overload conditions. An electronic thermal overload I
a thermal overload relay. This operation is based on three parameters; [Motor NP
FLA], [Motor OL Factor] and [Motor OL Hertz] (parameters 042, 048, and
047, respectively).
[Motor NP FLA] is multiplied by [Motor OL Factor] to allow the user to define
the continuous level of current allowed by the motor thermal overload. [Motor
OL Hertz] is used to allow the user to adjust the frequency below which the
motor overload is derated.
The motor can operate up to 102% of FLA continuously. If the drive was just
activated, it will run at 150% of FLA for 180 seconds. If the motor had been
operating at 100% for over 30 minutes, the drive will run at 150% of FLA for 60
seconds. These values assume the drive is operating above [Motor OL Hertz],
and that [Motor OL Factor] is set to 1.00.
Operation below 100% current causes the
temperature calculation to account for
motor cooling.
[Motor OL Hertz] defines the frequency
where motor overload capacity derate
should begin. The motor overload capacity
is reduced when operating below [Motor
OL Hertz]. For all settings of [Motor OL
Hertz] other than zero, the overload
capacity is reduced to 70% at an output frequency of zero.
Changing Overload Hz
120
100
80
60
40
20
0
0 10 20 30 40 50 60
% of Base Speed
[Motor NP FLA] is multiplied by [Motor OL 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. The effective overload
factor is a combination of [Motor OL Hertz] and [Motor OL Factor].
Changing Overload Factor
140
120
100
80
60
40
20
0
0 10 20 30 40 50 60 70
% of Base Speed
Rockwell Automation Publication 20B-UM002G-EN-P - July 2014
100000
10000
1000
100
10
100
OL Hz = 10
OL Hz = 25
OL Hz = 50
70 80 90 100
OL % = 1.20
OL % = 1.00
OL % = 0.80
80 90 100
2
T function emulates
Motor Overload Curve
Cold
Hot
125 150 175 200 225 250
Full Load Amps (%)