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Thermal defects widely occur in electrical equipment and affect its stable operation. This paper proposes a novel detection method based on derivatives for thermal defects of electrical equipment. First, the equivalent models of the equipment are established to analyze the surface temperature formed by different defects. Second, the theoretical foundation of the derivative-based detection method is described, and numerical calculations on thermal defect detection based on derivative characteristic curves are carried out. The results show that the method can detect the position effectively and calculate the depth with an error of 1.6%. Then, the thermal defects in different situations are analyzed, and the results indicate that the method is effective in all cases. Finally, the experiment is conducted by artificially preparing samples with thermal defects, and the achieved calculation error of the experimental results is within 3.3%, which indicates the validity of this method. [ABSTRACT FROM AUTHOR]

Contact wire is an essential part of traction power supply system in the electrified railway, which on the one hand transmits the electrical energy, and on the other hand plays as a smooth track for the current collection strip. In the daily operation of the electrified train maintenance, the contact wire suffers from the arcing ablation during the pantograph lowering process. Potential contact wire breakdown might take place. In this paper, the surface erosion of the contact wire by the pantograph arcing was studied numerically. A multi-physical model dedicated to the contact wire erosion issues was established, with the process of heat transfer, phase transition, and liquid metal flow taken into account. Characteristics of the surface erosion, the temperature field as well as the flow field under different current conditions were studied respectively. Particularly, the Marangoni effects on molten pool evolutions were examined, which could have a significant influence on the final erosion characteristics. This work might be helpful for the further understanding of the basic physical process of the contact wire erosion by the pantograph arcing, and as well as providing a meaningful reference for the performance improvement of the current collection system. [ABSTRACT FROM AUTHOR]