Menu 4 Introduction Parameter x.00
Parameter
description format
Keypad and
display
CT Modbus
RTU
User
programming
CT Soft Menu 0
Advanced parameter
descriptions
52 Commander SK Advanced User Guide
www.controltechniques.com Issue Number: 2
The temperature of the motor as a percentage of maximum temperature, with a constant current magnitude of I, constant value of K and constant
value of motor rated current (set by Pr 5.07 or Pr 21.07) after time t is given by
This assumes that the maximum allowed motor temperature is produced by K x Motor rated current and that τ is the thermal time constant of the point
in the motor that reaches it maximum allowed temperature first. τ is defined by Pr 4.15. The estimated motor temperature is given by Pr 4.19 as a
percentage of maximum temperature. If Pr 4.15 has a value of 0 the thermal time constant is taken as 1.
If the rated current (defined by Pr 5.07 or Pr 21.07 depending on which motor is selected) is less or equal to the Maximum heavy duty rating then
Pr 4.25 can be used to select 2 alternative protection characteristics (see diagram below). If Pr 4.25 is 0 the characteristic is for a motor which can
operate at rated current over the whole speed range. Induction motors with this type of characteristic normally have forced cooling. If Pr 4.25 is 1 the
characteristic is intended for motors where the cooling effect of motor fan reduces with reduced motor speed below half of rated speed. The maximum
value for K is 1.05, so that above the knee of the characteristics the motor can operate continuously up to 105% current.
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 0, the drive trips when
the threshold is reached. If Pr 4.16 is 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 falls below 95%.
Temp
I
2
K Motor rated current×()
2
-------------------------------------------------------------------------
1e
-t τ⁄
–()100%×=
Motor total
current (Pr 4.01)
as a percentage
of motor rated
current
Motor speed as a
percenta
e of base speed
100%
Max. permissible
continuous
current
100%
I t protection operates in this region
2
70%
50%
Pr = 0
Pr = 1
4.25
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
percenta
e of base speed
100%
Max. permissible
continuous
current
100%
I t protection operates in this region
2
70%
50%15%
Pr = 0
Pr = 1
4.25
4.25
Rated current (Pr 5.07 or Pr 21.07) ≤ maximum Heavy Duty rating.
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