Honeywell SmartVFD HVAC2 Applications Manual page 163

Mtp: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
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 2 x t6.
If the drive is in stop state the time constant is
internally increased to three times the set
parameter value. See also Figure "Motor
temperature calculation" on page 163.
The cooling in stop stage is based on convection
and the time constant is increased.
Motor temperature
105%
Motor
current
I/I
T
Fig. 61. Motor temperature calculation
163
Trip area
Time cons tant T *)
Q = (I/I T ) 2 x (1-e -t/T )
Motor temperature
*)
Changes by motor size and
adjusted with parameter
Fault/w arning
activation point,
if selected w ith
par. 12 .7
Time
12 .10
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