The lifetime of an electrical machine mainly depends on the thermal overloading. Modern day applications of electrical machines on one hand require compact machines with high power density, while on the other hand force electrical machines to undergo frequent temperature cycling. Until recently, in the case of electrical machines, the main factor related to the degradation of the winding insulation was thought to be the thermal oxidization of the insulation materials. It has now been revealed that thermal overloading can also induce mechanical stress in the windings of electrical machines, which over time could lead to fatigue and degradation. In this paper, a comprehensive study of the thermally induced mechanical stress in the windings of an electrical machine is presented. The study is performed using combined thermo-mechanical models. The numerical results are validated by experiments on a segmented stator winding set-up.

Thermal loading can induce mechanical stresses in the windings of electrical machines, especially those impregnated with epoxy resins, which is mostly the case in modern traction motors. Although designers look for cooling techniques that give better performance in terms of the power density and efficiency of the machine, several thermal cycles can lead to fatigue and the degradation of the copper insulation, epoxy and consequently the windings. In this paper, the performance of different cooling techniques has been compared based on the temperature distribution and the mechanical stress induced in the windings. Three-dimensional finite element thermo-mechanical models were built to perform the study. Two different variants of water jacket cooling, two configurations of direct coil cooling and two cases of combined water jacket and direct coil cooling methods have been considered in the paper. The results show that the combined water jacket and direct coil cooling perform the best in terms of the temperature and also the mechanical stress induced in the windings. An experimental set-up is built and tested to validate the numerical results.

A permanent magnet assisted synchronous reluctance machine (PMaSynRM) under static and dynamic rotor eccentricity has been studied, using the finite element method (FEM). Unlike the conventional star connected machine, a 5.5 kW machine with a combined star-delta winding configuration in the stator has been considered in this study. The impact of a combined star-delta configuration on the eccentricity forces and unbalanced magnetic pull of the PMaSynRM has been investigated, and a comparison with the conventional star connected machine has been presented. Moreover, other electromagnetic quantities of interest such as the magnetic flux density distribution and the induced back emf in the windings are also analyzed. Two prototype PMaSynRMs, having similar stator and rotor stack iron and geometrical parameters with two different stator winding, have been manufactured. The theoretical findings have been validated with measurements on the prototypes.

The power transformer is the most important element of equipment in an electrical transmission and distribution network. The power and voltage levels that these transformers can manage determine their size, and as the transformer's volume increases, internal isolation and cooling become more challenging. The most popular insulating fluid used in transformers for insulation and cooling is mineral-based oil, which has demonstrated exceptional dielectric and thermal qualities. However, alternative oil technologies have been sought to replace mineral-based oils in recent years because to concerns about safety, cost, and environmental impact. In this context, extensive research efforts have emerged on biological oils for use in transformers. This paper examines the sustainability, safety, and electrical performance of bio-based ester oil in transformer applications with respect to dissolved gas analysis (DGA). AI-based Fuzzy logic controller (FLC) with Duval's triangle (DT) and Duval's pentagon (DP), IEC, CIGRE reports are used in a hybrid manner to identify the possible incipient faults inside the oil-immersed transformers. The graphical analysis of various fuzzy logic plots along with DT and DP are utilized to critically analyze the possible incipient faults arrayed due to DGA. The proposed work proficient compared to previously published results. Highest efficiency of DT and DP based FLC (92%), followed by furan analysis (82.3%). Lastly, recommendations are made on potential fixes for the problems raised and the future course of study for alternate dielectric fluids-based power transformers. The suggested techniques in this research offer a higher diagnostic accuracy than the present approach.