Effective utilization of cables and transformers using passive filters for non-linear loads
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In the literature, it is well known that transformers and cables have excessive losses or overheating under non-sinusoidal current conditions. Accordingly, they have reduced current carrying capabilities (or loading capabilities) for that kind of conditions. This paper aims to employ passive filters for the effective utilization of the cables and transformers in the non-sinusoidal systems. Consequently, an optimal passive filter design approach is provided to maximize the power factor expression, which takes into account frequency-dependent line losses, under non-sinusoidal background voltage and line current conditions. The individual and total harmonic distortion limits placed in IEEE standard 519 are taken into account as constraints for the proposed approach. Besides, keeping the load's displacement power factor at an adequate range is desired by the proposed approach. The proposed approach and the traditional optimal passive filter design approach, which aims to maximize the classical power factor expression, are comparatively evaluated for an industrial power system with a group of linear and non-linear loads, overhead transmission lines, cables and a transformer. Numerical results show that the proposed one has a considerable advantage in the improvement of the total supply line loss and the transformer's loading capability under non-sinusoidal conditions when compared to the traditional one. On the other hand, for the simulated system cases, both approaches lead to almost the same current carrying capability value of the cables.