Siemens 420 manual Thermal motor protection and overload responses, Thermal motor model, Features

Issue 07/04 3 Functions

3.19Thermal motor protection and overload responses

Parameter range:	P0610 – P0614
	P0345
	r 0034
Warnings	A0511
Faults	F0011
Function chart number:	-

MICROMASTER 420 has a completely new integrated concept for thermal motor protection. There are numerous possibilities of effectively protecting the motor but at the same time ensuring high motor utilization. The basic philosophy of this innovative concept is to detect critical thermal states, output warnings and initiate the appropriate responses. By responding to critical states it is possible to operate the drive at the thermal power limit and to avoid, under all circumstances, an immediate shutdown (where the drive inverter is tripped).

Features

The protective concept distinguishes itself as a result of the following individual features:

Protection is effective without using any temperature sensor. The temperatures of various locations in the motor are indirectly determined using a temperature model.

Selectable responses P0610 which are to be initiated when the warning threshold is exceeded in order to prevent an overload condition.

The motor protection has been designed to be completely independent of the drive inverter protection. Warning thresholds and responses for drive inverter protection must be separately parameterized.

3.19.1Thermal motor model

The motor temperature rise increases because of the losses occurring during the energy-conversion process in the motor. These losses can be essentially sub- divided into two groups:

No-load losses

The no-load losses include the bearing and air friction losses as well as the re- magnetizing losses (eddy current and hysteresis losses). All of these loss components dependent on the speed and electrical frequency.

Load losses

The load losses are mainly determined by the thermal losses in the windings due to the current flowing through them.

An electrical motor represents a multi-material system (iron, copper, insulating material, air) where the heat source is especially concentrated in the windings, the laminated core and the shaft bearings. The following simplifications were made to replicate the thermal processes in the motor:

The motor is a homogenous body

Heat sources are uniformly distributed in the motor Heat is only dissipated using convection

MICROMASTER 420	Operating Instructions
6SE6400-5AA00-0BP0	135