Motor Overload - Rockwell PowerFlex 70 User Manual

Motor Overload

For single motor applications the drive can be programmed to protect the
motor from overload conditions. An electronic thermal overload I
function emulates 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 had
just been 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 Overload Curve
100000
10000
1000
100
10
100 125 150 175
Full Load Amps (%)
[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
% of Base Speed
Cold
Hot
200 225 250
50 60 70 80 90 100
Application Notes
OL Hz = 10
OL Hz = 25
OL Hz = 50
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