Function Applications
-518-
4.6.5 Overload Protection
To effectively protect motors with different loads, set the overload protection gain of motors based on
their overload capacity. The motor overload protection curve is an inverse time delay curve, as shown
in the following figure.
Figure 4-65 Inverse time delay curve of protection
When the running current reaches 175% of the rated motor current and the motor runs at this level for
2 minutes, or when the running current reaches 115% of the rated motor current and the motor runs at
this level for 80 minutes, the motor overload fault (E11.00) is reported.
1. Example 1
If the rated motor current is 100 A, when the running current reaches 125 A (125% of 100 A) and the
motor runs at 125 A for 40 minutes, the AC drive reports the motor overload fault (E11.00).
Note
The maximum overload time is 80 minutes and the minimum overload time is 10 seconds.
2. Example 2
The AC drive reports a motor overload fault after the motor runs for 2 minutes at 150% of the rated
current. As shown in the overload curve, 150% (I) of the rated current falls between 145% (I1) and
155% (I2) of the rated current. The overload fault reporting time for 145% of the rated current is 6
minutes (T1), and that for 155% of the rated current is 4 minutes (T2). Therefore, the overload fault
reporting time for 150% of the rated current is 5 minutes by default. The calculation is as follows.
“T = T1 + (T2 – T1) x (I – I1) / (I2 – I1) = 4 + (6 – 4) x (150% – 145%) / (155% – 145%) = 5 (minutes)”
To report the overload fault after the motor runs continuously for 2 minutes at 150% of the rated
current, set the motor overload protection gain according to the following calculation: F9-01 =
Desired overload protection time/Default overload protection time = 2/5 = 0.4.
Set F9–01 properly based on the actual overload capacity of the motor. Note that setting F9–01 to an excessively
high value may easily result in motor damage caused by overtemperature without warning.
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