Duty cycle for the motor overload – Rockwell Automation 20A PowerFlex 70EC/700VC User Manual
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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.
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.
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%.
FLA%
Cold Trip
Time
Hot Trip
Time
FLA%
Cold Trip
Time
Hot Trip
Time
FLA%
Cold Trip
Time
Hot Trip
Time
105
6320
5995
155
160
50
205
66
14
110
1794
1500
160
142
42
210
62
12
115
934
667
165
128
36
215
58
11
120
619
375
170
115
31
220
54
10
125
456
240
175
105
27
225
51
10
130
357
167
180
96
23
230
48
9
135
291
122
185
88
21
235
46
8
140
244
94
190
82
19
240
44
8
145
209
74
195
76
17
245
41
7
150
180
60
200
70
15
250
39
7
Changing Overload Hz
20
40
60
80
100
120
0
10
20
30
40
50
60
70
80
90 100
% of Base Speed
Contin
uous Rating
OL Hz = 10
OL Hz = 25
OL Hz = 50
20 Minutes
1 Minute
1 Minute
100%
150%