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Commander SK Advanced User Guide
69
Issue Number: 9 www.controltechniques.com
If the rated current is above the maximum Heavy Duty rating then Pr
4.25
can also be used to select 2 alternative protection characteristics. Both
characteristics are intended for motors where the cooling effect of the motor fan reduces with reduced motor speed, but with different speeds below
which the cooling effect is reduced. The maximum value for K is 1.01, so that above the knee of the characteristics the motor can operate
continuously up to 101% current.
When the estimated temperature reaches 100% the drive takes some action depending on the setting of Pr
4.16
. If Pr
4.16
is OFF(0), the drive trips
when the threshold is reached. If Pr
4.16
is On(1), the current limit is reduced to (K - 0.05) x 100% when the temperature is 100%. The current limit is
set back to the user defined level when the temperature (Pr
4.19
) falls below 95%.
The time for some action to be taken by the drive from cold with constant motor current is given by:
Alternatively the thermal time constant can be calculated from the trip time with a given current from
For example, if the drive should trip after supplying 150% overload (Pr
4.01
) for 60 seconds with K = 1.05 then
The thermal model temperature accumulator is reset to zero at power-up and accumulates the temperature of the motor while the drive remains
powered-up. Each time parameter Pr
11.45
is changed to select a new motor, or the rated current defined by Pr
5.07
or Pr
21.07
(depending on the
motor selected) is altered, the accumulator is reset to zero.
Motor total
current (Pr 4.01)
as a percentage
of motor rated
current
Motor speed as a
percentage of base speed
105%
Max. permissible
continuous
current
100%
It protection operates in this region
2
70%
50%
Pr
= 0
4.25
Pr
= 1
4.25
Rated current (Pr
5.07
or Pr
21.07
)
≤
maximum Heavy Duty rating.
Motor total
current (Pr 4.01)
as a percentage
of motor rated
current
Motor speed as a
percentage of base speed
101%
Max. permissible
continuous
current
100%
It protection operates in this region
2
70%
50%
15%
Pr
=
0
4.25
Pr
=
1
4.25
Rated current (Pr
5.07
or Pr
21.07
)
>
maximum Heavy Duty rating.
T
trip
- Pr 4.15
(
)
In 1
K Pr 5.07
×
Pr 4.01
------------------------------
⎝
⎠
⎛
⎞
2
–
×
=
Pr 4.15
-T
trip
In 1
K
Overload
-----------------------------
⎝
⎠
⎛
⎞
2
–
----------------------------------------------------------
=
Pr 4.15
-60
In 1
1.05
1.50
-----------
⎝
⎠
⎛
⎞
2
–
-----------------------------------------
89
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