75
6.11 Motor Overload Protection Function
In order to prevent the condition that the motor working damaged caused by overload for a long time or the VFD
rated current more than the motor rated current cause that the motor can’t be completely protected, the
SINUS MV
VFD is integrated with the motor overload inverse time limit protection function.
In: The rated current of motor
t: The time of inverse time limit overcurrent protection
k: Protection constant setting value
By expressions shows that when the motor current exceeds the rated current, inverse time limit protection
function will be activated. The larger the motor current is, the shorter the protection action time is. The sketch
map of inverse time limit protection as follows:
From the above chart shows, the inverse time protection is an integral process.The greater the overcurrent of
the motor, the greater the integral step, the shorter the VFD running time is. In order to quantitatively explain,
assuming that the output current of the VFD is constant at a certain overload multiplier of the motor, the VFD will
continue to run within corresponding time, until appears the corresponding fault.
SINUS MV
high voltage VFD and
duration are shown in the following table:
Figure 6-6 The sketch map of inverse time protection
Table 6-2 Motor overload multiple and duration corresponding table
Fixed overload multiplier
Approximate duration
110%~120%
1000s
120%~130%
125s
130%~140%
40s
140%~150%
12s
>150%
3s
