Application and Operation
6.12 Motor Overload
Product User Manual
Operating Instructions, Version AE 12/2009, A5E01454341C
135
manufacturer normally provides data for this curve. The control software uses the allowable
current level to determine the cooling capability of the motor.
If the user’s preference is to enter a fixed value of an allowable current level other than 100%
(as with the "straight inverse time" option), the speed-derating curve can be modified to have
the same desired level for all breakpoints.
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Figure 6-9 Default Speed Derating Curve showing Maximum Motor Load as Function of Speed
The plot in Figure " Drive Current (in percent of motor rated current) vs. Time taken for Motor
Temperature to rise from Rated Temperature to 120% of rated *" shows results from an
experimental evaluation of the software thermal model with the "straight inverse time" option
(100% "overload" setting) for various levels of drive current. A 4 kV, 300 Hp motor was used
for this test. The experimental data shows the time taken for the estimated motor
temperature to go from rated temperature to 120% of rated. This curve is quite conservative
as compared to a Class 10 TOL that trips at 280 sec with 150% current and at 630sec with
125% current.
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* The data was measured with the "straight inverse time" option.
Figure 6-10 Drive Current (in percent of motor rated current) vs. Time taken for Motor Temperature to
rise from Rated Temperature to 120% of rated *
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