Research on the Spatiotemporal Characteristics of Electromagnetic Force in Squirrel Cage Induction Motors with Rotor Bar Porosity
Chen Yi1, Deng Wenzhe1, Qian Zhe1,2, Li Guoli1,2, Wang Qunjing1,2
1. School of Electrical Engineering and Automation Anhui University Hefei 230601 China; 2. National Engineering Laboratory of Energy-Saving Motor and Control Technology Anhui University Hefei 230601 China
Abstract：Induction motors for EVs usually use die-cast aluminum or die-cast copper rotors. During the manufacturing process of rotor bars, material impurities and imperfections in the casting process ultimately result in porosity within the rotor bars. In the subsequent operation of the motor, the combined effect of electromagnetic force, thermal stress, and centrifugal force can also lead to the formation of porosity in the weak areas of the bars. When porosity reaches a significant level, broken bars can be generated, potentially leading to bearing damage and stator-rotor rubbing accidents. Therefore, this paper conducts a detailed study on the spatiotemporal characteristics of the additional electromagnetic force generated under the condition of rotor bar porosity in induction motors. Firstly, the spatiotemporal characteristics of the radial electromagnetic force of a healthy induction motor are analyzed. Then, according to the superposition principle, the superimposed current caused by the porosity fault is separated, and the equivalent of the additional magnetic field generated by the motor with porosity is realized by deducing the magnetomotive force generated by the superimposed current. The additional electromagnetic forces generated by the induction motor with various degrees of porosity in the bars are derived. The results show that the additional electromagnetic forces generated by the porosity fault have a significant impact on the magnetic field of the induction motor, introducing new orders and frequency components of radial electromagnetic forces, thus affecting the vibration and noise performance of the motor. Subsequently, through finite element simulation, the magnetic fields of the induction motors under healthy conditions and different bar porosity conditions are analyzed. The order and frequency characteristics of the additional electromagnetic force are obtained. At the same time, as the degree of porosity in the induction motor increases, the amplitudes of the characteristic components in the stator winding current and the radial electromagnetic force increase, exhibiting a linear relationship with the degree of porosity. When the pores are near the connection between the bar and the end ring, the closer to the connection, the smaller the fault. The degree of the fault is the lightest when the pores occur at the connection between the bar and the end ring. A fault motor simulation test bench is built with a 1.1 kW squirrel-cage induction motor. Experiments are conducted to measure stator currents and vibrations under healthy conditions and varying degrees of porosity and broken bars. The results show that the porosity fault of the induction motor leads to the appearance of characteristic components related to the slip rate of the motor in the stator winding currents and vibration signals. Varying porosity does not generate new characteristic components. The amplitude increases as the degree of porosity increases. The broken bar is an extreme case of the porosity fault of the motor. The sudden change of load and the sudden change of speed during the operation of the motor do not change the characteristic frequencies of the motor faults. The experimental results verify the theoretical derivation and simulation calculation. This study reveals the characteristic frequencies under the fault conditions, which are of great significance for the identification and diagnosis of rotor bar porosity in induction motors.
陈艺, 邓文哲, 钱喆, 李国丽, 王群京. 转子气孔条件下笼型感应电机电磁力时空特性研究[J]. 电工技术学报, 2025, 40(22): 7153-7165.
Chen Yi, Deng Wenzhe, Qian Zhe, Li Guoli, Wang Qunjing. Research on the Spatiotemporal Characteristics of Electromagnetic Force in Squirrel Cage Induction Motors with Rotor Bar Porosity. Transactions of China Electrotechnical Society, 2025, 40(22): 7153-7165.
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