Section 5: Configuration of the frequency converter
5.11. Electric motor rotation direction lock
It is possible to block the system to work only in one direction. Then,
regardless of the control signals, the system will rotate the motor only one
way. Parameter
1.65
allows you to specify this setting:
"0"
–
Reverse
—
two-way operation (default setting),
"1" –
Right —
one way work to the left,
"2" –
Left —
one way work to the right.
5.12. Thermal protections of the motor - Protection by I
2
t limit
The built-in thermal model of the motor enables to calculate the motor
temperature in the theoretical way. The model is developed on the basis of
the following assumptions:
•
the temperature of windings changes according to the exponential
law,
•
the electric motor achieves the maximal temperature for continuous
work at a nominal current,
•
the temperature rise depends on the ratio (I/In)
2
,
•
the cooling time constant for the stopped motor is four times higher
than the heating time constant during operation.
Relative
long-term motor current
for frequencies above 25Hz is determined
by
parameter 3. 03
. For frequencies below 25Hz, the long-term current is
lower (lower efficiency of the cooling fan placed on the motor shaft) and
determined by
parameter 3. 04
. These parameters are determined in relation
to the nominal motor current for 100. 0% = In. This is how the
long-term work
area
is determined (Fig. 5.7a).
When cooling the motor without additional ventilation (only internal fan), set
par. 3.04 to 35% of the nominal motor current. If additional engine ventilation
is used, the value of par. 3.04 can be increased up to 75%. If the motor
current is not within the defined long-term operating range, the calculated
temperature will increase above 100%.
When the calculated temperature
reaches 105%, the system will be switched off
(a failure message will be
displayed). This situation takes place in Fig. 5.7c for the increase in
temperature marked with a dashed line.
The rate of increase of the calculated temperature is specified by
parameter
3.05
- time constant of motor heating. This is the time after which the motor
temperature reaches 63% of the final temperature increase value. In practice,
it is possible to set par. 3.05 = 120 * t6 [min], where t6 [s] is given by the
motor manufacturer.
TWERD Power Electronics
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