Asinhrono elektrodzinēju termiskā stāvokļa noteikšanas risinājumi to ekspluatācijas drošuma paaugstināšanai: promocijas darba kopsavilkums zinātnes doktora (Ph.D.) zinātniskā grāda iegūšanai

The aim of the scientific thesis: theoretically and experimentally validate the method of estimating the stator winding temperature of an induction motor with remote measurement of motor rotation frequency and to develop an algorithm for application of this method for protection of low power induction motors against overheating. The following tasks have been set to achieve the aim of the work: 1. to perform the analysis of the induction motor heating process, power losses and determination of thermal parameters on induction motor; 2. to study the methods of determining the stator windings temperature of induction motors; 3. to develop a mathematical model of low power induction motor stator windings heating process; 4. to perform experimental research of heating of induction motors operating at constant load with different rotor rotation frequency under normal conditions and under various cooling disturbances; 5. to develop a mathematical model describing the stator winding temperature and rotor rotation frequency changes; 6. verification and validation of the developed mathematical model – comparison of the simulation results with experimental results; 7. development of algorithm for low power induction motors protection and technical economic evaluation of the developed stator winding detection method to improve safety and reduce failure of induction motors used in agricultural production. The paper consists of 5 chapters: Chapter 1 analyses the problems of induction motor failures, their types, causes and statistics in all industrial sectors and agricultural sectors, analyses the statistics of induction motor failures and their causes in henhouses at “Balticovo” egg processing plant in Iecava, discusses the types and comparison of induction motor protection methods. Chapter 2 discusses the types of heat losses of induction motors and their calculation, the basics of induction motor heating processes, the influence of different electric motor operating modes on their heating and stator winding temperature determination methods. In Chapter 3, experimental studies of induction motor heating under different loads and cooling conditions are performed, the correlation of stator winding temperature and rotational frequency changes are analysed and empirical model is obtained, which can determine stator winding temperature changes by estimation rotational frequency of induction motor. Chapter 4 discusses the first-order heating model of an induction motor and evaluates its accuracy, a second-order heating model is developed to improve the stator winding temperature estimation model, comparison of the improved model simulation results with experimental results. In Chapter 5, modelling of induction motor’s reliability is performed, the rotational frequency estimation methods of using motors using current sensors are described, the algorithm for stator winding temperature estimation device is described, and the economic evaluation of this device implementation is performed. The results of research and modelling confirm the hypothesizes that the winding temperature and rotor rotation frequency of induction motor are influenced by cooling conditions and using remote measurement of electric motor rotor rotation frequency, it is possible to protect electric motor stator winding from overheating.