f
f
n
P13.9=40%
0
I
T
100%
Overload area
P
cooling
Corner freq
parameter descriptions vacon
•
129
9
Figure 9.17: Motor thermal current IT curve
13.10 M
TP
:
THERMAL
TIME
CONSTANT
This time can be set between 1 and 200 minutes.
This is the thermal time constant of the motor. The bigger the frame and/or
slower the speed of the motor, the longer the time constants. The time con-
stant is the time within which the calculated thermal model has reached 63%
of i
ts final value.
The motor thermal time is specific to the motor design and it varies between
d
ifferent motor manufacturers.
If the motor's t6-time (t6 is the time in seconds the motor can safely operate
a
t six times the rated current) is known (given by the motor manufacturer) the
time constant parameter can be set basing on it. As a rule of thumb, the motor
thermal time constant in minutes equals to 2 x t6. If the drive is in stop state
the time constant is internally increased to three times the set parameter val-
ue. See also Figure 9.18.
The cooling in stop stage is based on convection and the time constant is in-
creased.
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