Two-Channel Thermodynamic Model of the Induction Motor for the Heat Protection System
The article describes the approach to constructing a thermal protection system for an induction motor based on the separation of thermodynamic processes into fast and slow. The structure of a two-channel thermodynamic model is substantiated, in which this principle of process separation is realized and the mathematical description of such a model is obtained. The advantage of the proposed approach is a small amount of initial data necessary for the parameterization of the thermal protection system. The proposed version of the thermal protection system uses a two-mass thermodynamic model of the motor to calculate the stator winding temperature rise above the ambient temperature, and at the same time providing a simpler solution to the problem of setting the initial conditions for starting the protection system after a break than the thermal control system of the electric motor using traditional thermal models. The problems of the proposed thermodynamic model parameters determining are considered. The values of fast and slow channel time constants for enclosed induction motors of different power are given. The approach to the account of the speed changes effect on motor cooling is set out. The influence of the error arising from the transition from the initial thermodynamic model (the two-mass model of the traditional type) to the model transformed to the two-channel version is analyzed. The algorithm of the thermal protection system operation based on the two-channel model for the situations of slow temperature increase and for short-term strong overload is described. The features of determining the initial conditions for the thermodynamic model under consideration after a break in the operation of the system are noted. The results of simulation of this protection system in Matlab/Simulink are given.