Honeywell SmartVFD HVAC MR4 User Manual page 145

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M3.9.9 M
OTOR THERMAL TIME CONSTANT
This is the thermal time constant of the motor. The bigger the motor, the bigger the time con-
stant. The time constant is the time within which the calculated thermal stage has reached 63%
of its final value.
The motor thermal time is specific to the motor design and it varies between different motor
manufacturers. The default value of the parameter varies from size to size.
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 2*t6.
If the drive is in stop stage the time constant is internally increased to three times the set pa-
rameter value. The cooling in stop stage is based on convection and the time constant is in-
creased.
See Figure 15.
M3.9.10 M
OTOR THERMAL LOADABILITY FACTOR
Setting value to 130% means that the nominal temperature will be reached with 130% of motor
nominal current.
P cooling
Overload area
100%
Par.
M3.9.8=40%
0
Figure 14. Motor thermal current I
f
Corner freq f
n
100K2 8
curve
T
HVAC A
PPLICATION
I
T