Siemens 420 manual 136

3 Functions Issue 07/04

Using these simplifications, the thermal motor behavior can be defined using a 1st 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:

0No response, only a warning

1Warning and Imax is reduced

(this results in a lower output frequency)

2Warning and fault (F0011)

Trip threshold 1.1⋅ P0614

P0611

r0027 2

   P0305 

r0021

P0310

		Motor
			F0011
	r0034	i2t
		temp.	I_max reduction
	( i2 t )
t		reaction
		P0610	A0511

P0335

P0614

Warning threshold

Fig. 3-56 Drive inverter response

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.

MICROMASTER 420	Operating Instructions
136	6SE6400-5AA00-0BP0