Motor Overload 2-119
3. [Motor OL Hertz] is used to further protect motors with limited speed
ranges. Since some motors may not have sufficient cooling ability at
lower speeds, the Overload feature can be programmed to increase
protection in the lower speed areas. This parameter defines the frequency
where derating the motor overload capacity should begin. As shown
here, the motor overload capacity is reduced when operating below the
motor overload Hz. For all settings of overload Hz other than zero, the
overload capacity is reduced to 70% when output frequency is zero.
During DC injection the motor current may exceed 70% of FLA, but this
will cause the Motor Thermal Overload to trip sooner than when
operating at base speed. At low frequencies, the limiting factor may be
the Drive Thermal Overload.
Changing Overload Factor
20
40
60
80
100
120
140
0 102030405060708090100
% of Base Speed
Continuous Rating
OL % = 1.20
OL % = 1.00
OL % = 0.80
Changing Overload Hz
20
40
60
80
100
120
0 102030405060708090100
% of Base Speed
Continuous Rating
OL Hz = 10
OL Hz = 25
OL Hz = 50
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