Eaton Cutler-Hammer SLX9000 Series, User Manual

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SLX9000 Adjustable Frequency Drives User Manual
9-26
For more information visit: www.eaton.com MN04003020E
January 2009
Figure 9-18: Motor Cooling Power
2.7.9 Motor thermal protection: Time constant ID707
This time can be set between 1 and 200 minutes.
This is the thermal time constant of the motor. The bigger the motor, the bigger the
time constant. The time constant is the time within which the calculated thermal
model has reached 63% of its final value.
The motor thermal time is specific to the motor design and it varies between
different motor manufacturers.
If the motor’s t6-time (t6 is the time in seconds the motor can safely operate at 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 2xt6. If the drive is in stop state, the time constant
is internally increased to three times the set parameter value. The cooling in the stop
state is based on convection and the time constant is increased. See also
Figure 9-19 .
Note: If the nominal speed (par. 2.1.8) or the nominal current (par. 2.1.9) of the motor
are changed, this parameter is automatically set to the default value (45).
100 %
0
Overload Area
Par.
ID706=40
%
Cooli n g
P
f
f
n
I
T