Honeywell HVAC232 Series, Applications Manual

Page: 124 / 145

Application manual HVAC232/402 | Document 27-652 | Issue ENG06 | 2019-08-07 124
Motor thermal protection (Mtp): Zero speed cooling
Defines the cooling factor at zero speed in relation to the point where the
motor is running at nominal speed without external cooling. The default
value is set assuming that there is no external fan cooling the motor. If an
external fan is used this parameter can be set to 90 % (or even higher).
If you change the parameter P1.4 (Motor nominal current), this parameter
is automatically restored to the default value. Setting this parameter does
not affect the maximum output current of the drive which is determined by
parameter P1.7 alone.
The corner frequency for the thermal protection is 70% of the motor nomi-
nal frequency (P1.2).
The cooling power can be set between 0…150.0% × cooling power at nomi-
nal frequency. See below:
P13.9 = 40%
100%
f
f
n
0
I
T
Pcooling
Corner
frequency
Overload area
Fig. 60. Motor thermal current I
t
curve
Motor thermal protection (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 × t6. If the drive is in stop state the time constant is internally increased to
three times the set parameter value.
The cooling in stop stage is based on convection and the time constant is
increased. See also figure below.
*)
105 %
Q = (I/IT)2 x (1-e-t/T)
I/I
T
Motor temperature
Time
Motor temperature
Trip area
Changes by motor size and adjusted with parameter P12.10
Fault/warning
activation point,
if selected with
par. 12.7
Motor
current
Time constant T*)
Fig. 61. Motor temperature calculation