Allen-Bradley PowerFlex 70 Enhanced Control Reference Manual page 60

56 Motor Overload
3. [Motor OL Hertz] is used to further protect motors with limited speed ranges.
Since many motors do 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. For all settings of overload Hz other than zero, the
overload capacity is reduced to 70% when output frequency is zero. During DC
injection braking, the motor current may exceed 70% of FLA, but this will cause
the motor overload to trip sooner than when operating at base speed. At low
frequencies, the limiting factor may be the drive overload rather than the motor
overload.
Changing Overload Hz
120
100
80
60
40
20
0 10 20 30
Duty Cycle for the Motor Overload
When the motor is cold, this function will allow 3 minutes at 150%. When the
motor is hot, it will allow 1 minute at 150%. A continuous load of 102% is allowed
to avoid nuisance faults. The duty cycle of the motor overload is defined as follows.
If operating continuous at 100% FLA, and the load increases to 150% FLA for 59
seconds and then returns to 100%FLA, the load must remain at 100% FLA for 20
minutes to reach steady state.
1 Minute
150%
100%
20 Minutes
The ratio of 1:20 is the same for all durations of 150%. When operating continuous
at 100%, if the load increases to 150% for 1 second the load must then return to
100% for 20 seconds before another step to 150%.
Cold Trip Hot Trip
FLA% Time Time
105 6320 5995
110 1794 1500
115 934 667
120 619 375
125 456 240
130 357 167
135 291 122
140 244 94
145 209 74
150 180 60
40 50 60 70 80 90 100
% of Base Speed
1 Minute
Cold Trip Hot Trip
FLA% Time Time
155 160 50
160 142 42
165 128 36
170 115 31
175 105 27
180 96 23
185 88 21
190 82 19
195 76 17
200 70 15
OL Hz = 10
OL Hz = 25
OL Hz = 50
Cold Trip Hot Trip
FLA% Time Time
205 66 14
210 62 12
215 58 11
220 54 10
225 51 10
230 48 9
235 46 8
240 44 8
245 41 7
250 39 7