This paper presents a new approach to investigation of interharmonics in power supply systems. Interharmonics are generated by industrial customers in transient processes and most often in cases when amplitude modulation of current and voltage takes place. Main sources of interharmonics are arc furnaces, electric arc welding and thyristor drive with frequency regulation of rotation speed. Interharmonics appear also in rolling mill electrical networks during sudden increases and decreases of load current and if strong saturation of transformers and series or parallel reactive power compensation take place. Using Fourier transform instead of Fourier series expansion is recommended for analysis of interharmonics.
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