No abstract

This study deals with the influence of voltage subharmonics and interharmonics on an induction cage machine. The windings current subharmonics and interharmonics as well as the magnetising current are studied. The effect of voltage subharmonics and interharmonics on windings temperature rise is analysed. The results of measurements and calculations are compared for various machine models. The appropriate investigations are performed for two low-power, totally enclosed induction motors of different properties: a machine with a comparatively strongly saturated magnetic circuit, and one with a comparatively weakly saturated magnetic circuit.

In a power system, the voltage waveform usually contains harmonics and sometimes interharmonics, often defined as components of frequency greater than the fundamental voltage component but not of its integer multiple. Previous studies have reported a minor effect of voltage interharmonics on a cage induction machine. This paper reveals their extraordinary harmfulness for induction motors. Namely, voltage interharmonics may cause high vibration, which can result in machine damage. In addition, interharmonics can lead to torque pulsations corresponding to the natural frequency of the first elastic mode. Consequently, possible torsional resonance may cause destruction of a power train. In this study, the results of investigations on undesirable phenomena due to interharmonics are presented for seven motors with a rated power 3 kW–5.6 MW.

This project is financially supported under the framework of a program of the Ministry of Science and Higher Education (Poland) as "Regional Excellence Initiative" in the years 2019-2022, project number 006/RID/2018/19, amount of funding 11 870 000 PLN.

Sinusoidal voltage fluctuations can be considered a specific result of the occurrence of voltage subharmonics and interharmonics, which are components of low frequency or not being an integer multiple of the frequency of the fundamental voltage harmonic. These components—symmetrical subharmonics and interharmonics—are of the same magnitude, while their frequencies are symmetrical with respect to the fundamental frequency. Depending on their phase angles, various kinds of voltage fluctuations can be distinguished: amplitude modulation, phase modulation and intermediate modulation. In this study, the effect of phase angles on noxious phenomena in induction motors was analyzed. Additionally, torque pulsations and vibrations of an induction motor under sinusoidal voltage fluctuation and a single voltage subharmonic or interharmonic were compared. The investigations were performed with the finite element method and an experimental method. Among other findings, it was found that for some phase angles torque pulsations could be about ten times higher than for other angles, roughly corresponding to the amplitude modulation.