Thermal State Analysis of Adjustable Speed Induction Motor

Abstract

An equivalent thermal circuit is presented, which makes it possible to analyze the thermal state of a speed-controlled induction motor fed by a PWM voltage-source inverter in static and dynamic modes. It is taken into account that the losses in the structural elements of the engine and thermal conduc- tivity, the values of which depend on the speed, change at different points of the control range. The tempera- tures of seven structural elements of the machine are determined: the stator steel package, the groove part of the stator winding, the rotor, the frame, the internal air, the end shields, and the frontal part of the stator winding. Theoretical and experimental studies of thermal indicators - the temperature of the stator winding frontal part and the temperature of the bearing shield of the AIP71A2 induction motor with self-cooling were carried out. The temperature characteristics are determined, which are the dependences of the over- heating of the structural parts of a frequency-controlled induction motor on the load torque for different fre- quencies of the supply voltage. These characteristics are compared with those obtained from thermal exper- iments. Non-stationary heat calculations are performed by solving a system of differential heat balance equations. The transition to temperature control characteristics has been completed. Thermodynamic processes are considered theoretically and experimentally during the operation of a controlled drive at a given tachogram. Thermodynamic characteristics are determined by load tachograms and can be plotted for different intermittent modes.