In modern industries, enhancing the efficiency and performance of electric motors is a critical requirement. Pulse-width modulation (PWM) inverters utilized to enhance the energy efficiency of electric motors generate complex shaft voltages and bearing currents, leading to bearing electrical erosion. This study proposes a new method for detecting high-frequency (HF) circulating current and electric discharge machining (EDM) current signals in bearings for electric motors. The proposed method utilizes common mode voltage (CMV) and bearing current data, analyzing the relationship between these signals. Subsequently, it applies filtering techniques and differentiation for signal preprocessing. The interquartile range (IQR) method is used to detect outliers, classify HF circulating current and EDM current signals, and perform time-series data clustering to determine the occurrence frequency and timing of EDM signals. Finally, the implementation outcomes of the proposed method are validated, and its classification efficacy is evaluated and benchmarked against established methodologies through a comprehensive performance analysis. The proposed technique is anticipated to be applicable to the maintenance and prediction of modern electric motors in future developments, contributing to enhanced durability and reliability.

Effects of main and trace elements on the formation of oxide in the oxidation behavior of Inconel 600 and 625 were investigated in this study using various calculated phase diagrams. After the isothermal oxidation tests at 1000 and 1100 °C, Nickel 201 for comparison showed significant growth of an oxide layer corresponding to NiO, and the NiO layer consisted of oxide crystals with both equiaxed and columnar shapes. As the temperature increased, the growth of the oxide layer proceeded mainly through columnar crystals. On the other hand, Inconel 600 and 625 showed relatively thin oxide layers, which were confirmed to be mainly composed of Cr₂O₃. The Cr₂O₃ layer was composed of equiaxed fine crystals. In the case of Inconel 625, an intermediate layer was formed at the interface between Cr₂O₃ and the base metal. It was found that the surface segregation of Cr as the main alloying element influenced the formation of the oxide layer of two Inconel alloys, and that some elements disappeared from the base metal near the surface due to continuous surface segregation and vaporization. On the other hand, even some elements with trace amounts showed strong surface segregation and contributed to the formation of oxide layer.