2nd edition, 31-03-2020
7000.05061, 2nd edition, 31-03-2020
7000.05061
Description of functions
36
5.5
Protective functions
5.5.1
I
2
t current limitation
I
2
t current limitation protects the motor against overheating. A thermal current model
which calculates the motor temperature is created for this purpose. The motor current is
influenced depending on the calculated temperature. The following values are relevant for
I
2
t current limitation:
Peak current (I
max
):
The current is limited to the peak current for as long as the thermal current model cal-
culates a non-critical temperature.
Continuous current (I
cont
):
The current is limited to the continuous current if the thermal model calculates a critical
temperature.
Functionality of the I
2
t current limitation
The functionality of I
2
t current limitation is explained below with the aid of an example.
Fig. 19: Example of I
2
t current limitation
Area I:
When the motor is started, the peak current is preset as the set value at the current con-
troller.
As the load (X
1
) increases, the current in the motor becomes higher and higher until the
peak current (I
max
) is reached.
The current controller comes into effect and limits the motor current to the peak cur-
rent (I
max
). At the same time, the flowing current is used to calculate a model tempera-
ture in a thermal current model.
crit
T
model
T
I
cont
I
max
I
t
t
X
1
X
2
I
II
III
