Preloading; Thermal Model Selection; Alarm And Tripping Limits - ABB DCS 500B Description

Preloading

Thermal model
selection
Alarm and trip-
ping limits
DCS 500 Software Description
When the motor is cooling, the temperature model follows the for-
mula
Iact 2
=  * e -t/τ ) * 100
Q act
I ref 2
As can be seen from formulas (1) and (2) , the thermal model uses
the same time constant for a warming motor and a cooling motor.
Formulas 1 and 2 do not take into account the thermal preloading
which in practical cases precedes currents that are higher than the
rated current. In the model these can cause a trip.
Preloading current is I 0.
I act 2 - I 0 2
Q act =  * ( 1 - e -t/τ ) * 100
I ref 2 - I 0 2
The activation of thermal model is made by parameters
MODEL1.SEL (1405) and MODEL2.SEL (1605). If the thermal
model is not activated (0), its output is set to zero.
Input signal [MOTOR2] (913) selects which of the thermal models
follows the armature current measurement.
[MOTOR2] (913)
0 = MODEL 1 follows the armature current measurement
1 = MODEL 2 follows the armature current measurement
One thermal model thus follows the armature current and the other
is cooling.
Alarm and tripping limit calculation uses as the base current (I ref )
the values given by parameters
MODEL1.CURR (1406)
MODEL2.CURR (1605)
The normal value is 4096 (≅ motor rated current). This value should
not normally be changed. If for some reason it is not possible to run
the motor continuously with rated current, e.g. due to poor cooling
environment, then the value can be decreased. E.g. the target
continuous load is 85% of the used motor rated current. Then the
parameters are 0.85 * 4096 = 3481.
Functional Software description
(2)
(3)
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