Siemens MICROMASTER 420 Operating Instructions Manual page 136

3 Functions
Using these simplifications, the thermal motor behavior can be defined using a 1
Order filter (PT1 filter). In this case, the square of the normalized motor current
(measured motor current r0027 divided by the rated motor current P0305) weighted
by the thermal motor time constant P0611 results in the I²t value of the motor
r0034. The I²t value represents a parameter for the temperature rise / temperature
of the motor.
In addition, the output frequency (motor speed) is included in the calculation in
order to take into account the cooling effect of the motor fan.
If parameter P0335 is changed to a force-ventilated motor, then the calculation is
also appropriately modified.
If the I²t value of the motor (r0034) reaches the value defined in P0614 (default:
100%), alarm message A0511 is output and depending on P0610, a response is
initiated, or, when the shutdown threshold is reached, a fault. The following settings
are possible for P0610:
0 No response, only a warning
1 Warning and Imax is reduced
(this results in a lower output frequency)
2 Warning and fault (F0011)
Fig. 3-56
The thermal motor time constant P0611 is a measure for the rate at which the
motor temperature changes and must be entered depending on the motor.
NOTE
For motors with a higher weight P0344, the temperature increase characteristic
is significantly slower than for small motors.
If thermal data of a third-party motor is not entered, then values are used that
are based on a Siemens motor.
Thermal motor data should be taken from the appropriate motor Catalogs.
136
P0611
2
 
r0027
 
P0305
 
t
r0021
P0310
P0335
Drive inverter response
Trip threshold
1.1 P0614
Motor
F0011
i2t
r0034
temp. I_max reduction
2
i ( ) t
reaction
A0511
P0610
P0614
Warning threshold
MICROMASTER 420
Issue 07/04
st
Operating Instructions
6SE6400-5AA00-0BP0