ANALYSIS OF THERMAL PROCESSES OCCURRING IN TRACTION ELECTRIC MACHINES DURING HEATING TESTS

Purpose. It is known that during acceptance tests, which are carried out in accordance with the requirements of DSTU GOST 2582:2017, the thermal load of the windings of engines and generators can differ significantly, which affects the accuracy of the results obtained. The nature of the thermal load itself largely depends on the test scheme and the method of covering power losses in electric machines. Studies of thermal processes occurring in the windings of traction electric machines during their heating tests are timely and relevant. The purpose of the scientific research is to develop and scientifically substantiate a method for assessing the degree of difference in thermal loads of the armature windings and excitation windings of a pair of mutually loaded tested traction electric machines, Methodology. The analysis of thermal processes in the active parts of traction electric machines during their heating tests was performed using the theory of heating of a homogeneous solid and known methods for calculating thermal schemes. Findings. It was established that the thermal potential of electric machine windings is determined by both electrical power losses in the windings and magnetic power losses in the magnetic core. The influence of each type of loss on the overheating of the windings was considered, and a simplified thermal equivalent scheme was proposed for the qualitative analysis of these processes. Studies have shown that electrical losses have a dominant influence on the formation of the thermal potential of the windings, while the influence of magnetic losses is much smaller - the ratio of the relative coefficient of influence of electrical losses to the coefficient of influence of magnetic losses is equal to three. А method for determining the degree of influence of overload or underload by current and magnetic flux on the temperature of the armature windings is proposed. The method takes into account the parameters of losses in hourly and long-term operating modes of traction electric machines. Special attention is paid to the difficulties of calculating non-stationary thermal processes and the possibility of their qualitative analysis using simplified models. Originality. A scientifically substantiated method for assessing the degree of difference in thermal loads of the armature windings and excitation windings of a pair of mutually loaded tested traction electric machines is proposed, which determines the quality of the test. Graphical dependences of the specific temperature rise of the armature of the tested motor on the specific losses in copper and steel, in particular for the NB-406 traction motor, are obtained. The results obtained indicate the adequacy of the proposed methodology and its compliance with real test conditions. Practical value. The scientific results obtained in the work can be used in improving the methods of thermal testing of traction electric machines. Their use allows to increase the accuracy of the assessment of thermal processes in electric machines and ensure their compliance with operating conditions and improve the quality of tests. The proposed methodology can be used as one of the criteria for choosing a rational variant of the mutual loading scheme.